Has anyone got any experience with the baby "jump start" battery boxes?

Right now specifically interested in using one as a 12V power source for the alarms and anti theft devices on Her Ladyships BMW K1200LT which flatten the bike battery in about 6 weeks - 2 months. Garage in separate block so no power. I figure that she can easily pull something that small and, basically, portable off every week and take it back to her flat to recharge overnight. Presumably when it goes back on again it will top up the main battery whilst looking after the alarms et al. If I find one that works for her I plan to get one to do same job on my P38, which usually needs a top up charge a couple or four times a year if I'm not out and about much.

Problem is deciding on what is a good brand, which capacity specification to believe and whether a separate 12 DC output alongside the jump start one is useful. far as I can see most of the usual suspects quote the capacity for the USB 3.2 / 5V output in milli amp hours to get nice big numbers. Real 12 volt capacity seems to be around 1/3 of those numbers. Say 1 1/2 to 3 amp hours for the under £100 market.

Clive

I bought a cheapo Chinese one on eBay that claimed to have a capacity of 82,000 mAh. I took that to be similar to Italian horsepower as 82 Ah is pretty good for a full sized car battery. However, it worked well and started the Ascot, the SE and a number of other cars. Then one day it decided it didn't want to charge and did nothing. Took it apart and found a stack of Li-ion packs, one of which was twice the thickness of the others. So, I can't recommend a brand, just avoid the cheapo ones (although I suspect if it was used as you describe rather than to start a 4.6 litre V8, it might survive anyway).

Thanks for that information. Pretty much what I expected so gonna be pot luck. Decisions, decisions!

£35 cheapy or £80 for one with a separate 12 volt power bank output off t'Bay. Or wait until next time round at LiDL as their Ultimate Speed branded one looks adequate VFM with a warranty. Certainly the little LiDL battery chargers are quite decent. Always bit of crap-shoot for boy-toy things out of LiDL. The good stuff is more than decent, especially given the price, but the not so good usually re-defines horrible.

On the bricks and mortar side EuroCar have an offering and Halfrauds list several, albeit the apparently decent ones seem expensive and not on shelf at the nearest branch.

Clive

As well as the 12V starter output, the one I bought had a 19V output for a laptop (along with multiple connectors to fit different laptops) and 4 USB sockets. I figured that as well as being able to use it to start a car, I could use the USB outputs when on my European trips. I use an Android tablet with data SIM for streaming audio which feeds into a headphone amp (as the output from the tablet alone isn't high enough for the line in on the car stereo) as well as my phone which all need a USB supply for charging. I figured one big supply would make life easier. Unfortunately, I killed it before getting the chance to try it.....

Its one of those things that might actually be better shopping for on Amazon as you can look at reviews to get an idea if your getting a decent one or not. The ones they used to sell in Maplin and the like were fairly hopeless (sealed lead acid battery inside like you'd find in a computer UPS, not the right thing for the job at all and would work a few times and then give up rapidly).

My mother has one, which seems to work for jump starting when required, doesn't get so much use now as it did, but did work provided it had been charged (her car didn't used to get much use as it was the second car, so would frequently need a jump to get going). Not sure if you'd get much of a charge by leaving it connected all the time, but it might stop some of the discharge at least.

Used a 'SAKURA' 7500mAh for a while now with reasonable success but not exactly to 'jump start. engines...
as usually I connect it up to the main battery for about 10-15 minutes and then disconnect it and start it up.
Never tried it with the main battery absolutely flat as I expect it is far too much to ask for one of these boxes:
Should be fine used to 'trickle' the battery for a week or so (depending on the state of the battery on the bike)

Personally I've usually got a charged spare battery sitting around somewhere handy and a set of jump leads anyway, so would rarely find a need for one. Not quite as portable, but does work all the same.

I'd much rather have one of the 'traditional' types with one or two SLA batteries in it. A decent one mind, not the crap from Maplin, Argos or halfords. Sure they're big and heavy, but far less likely to suffer thermal runaway and explode than a highly strung lithium pack being asked far too much of.

Machinemart sell a range of decent SLA based ones. I have both their old 900, which is a single 18ah battery, and the 12/24v one which is a pair of 22ah batteries. On 12v, you get 44ah of power as they're wired in series through the selector switch.

I keep my snap on pack handy, it’s never let me down, old and heavy in comparison to today’s jump packs, Keep an eye out nowadays and there’s some bargains to be had

A lot of these devices rely on the fact that a car battery often isnt actually flat, its just discharged by enough to be unable to get "over the hump" required to get the engine turning.

Even actual jump leads fall into this category. My mate had an issue recently where the starter feed from the rear mounted battery in his BMW had broken. He tried to jump start it and got nothing. The engine wouldnt even turn. The AA came out with proper jump leads and the car started immediately. When i popped round i looked at his jump cables and despite having a nice thick jacket, the actual copper core was about 6mm^2.

If you look at a typical LiPo pack for an RC car you can get an idea about how actual decent Lithium batteries can perform:

https://hobbyking.com/en_us/turnigy-5000mah-4s-40c-lipo-pack-with-xt90.html

This ones rated 5AH and is a "4S" pack (so 4 cells in series) rated around 14v, however it has a maximum discharge of 40c, which is around 200A.

Clearly, these batteries are capable, they are both more energy dense than a lead acid, while also having a much larger maximum discharge for a given capacity, and a properly designed jumper pack using decent cells would very likely be able to jump start a car with a completely flat battery.

The issue ofcourse is that many of these batteries are sold by shonky chinese sellers, using poor quality or lowly rated cells.

I would find yourself a "group test" type review that does decent testing and have a bit of a compare, heres one example:
https://www.autoexpress.co.uk/accessories-tyres/92728/best-mini-jump-starter-packs-2019

But try to find a few reviews and cross reference the results.

Thanks for the help. Great link to the group test puts things into perspective.

Gotta admit that these high capacity small packs scare me. 20 year old Clive spent an "interesting" month doing load / power delivery tests on thermal batteries. Having both battery and load glowing red hot on the bench in front of you after a 5 minute full load discharge test rather makes the point about high current issues. 5 minutes being always long enough for an anti-tank missile.

Naturally having got it all together Her ladyship has changed her mind! She is going to take the battery off over winter and keep it in the flat hooked up to a maintaining charger.
Wimmin.
Still think I might get one for me tho'.

Clive

I am a bit late to the party but I bought a Clarke jump start a couple of years ago when It was on offer from Machine Mart. It has an impressive spec (on paper).

https://www.machinemart.co.uk/p/jump-start-4000/

Bearing in mind I have the diesel, which is a whole new ball game as regards starting, It said 1500 amps and the battery on the car is about 1000 CCA, so I thought it would be man enough. However it would hardly turn over the car even after fully charging the jump starter.
I have a professional battery tester and it only gave 180 Amps. The shop swapped it for another but it was no better. I got a refund.
I can't see how it could ever be rated at 1500 amps.

Unfortunately Clarke used that 'magical marketing word' there - "peak" ! (and for all they care that might just be for a second...)

Inside these is typically a small lead-acid battery, the kind you might find on a moped.... well (notionally) 42Ah anyway, at least if you keep it chaged up properly: I have used one of these too, again using my technique above on a main battery with the "not-quite-enough-grunt to-crank" situation (Connect the box for 10-15 minutes to the main battery, disconnect it, try again)

These latest 'baby' jump start boxes have Li-Ion batteries within of course, so not exactly designed to pump out 100 amps for 10 seconds or so either...

Let's look at the MF31 battery for a second, that puts out 1000 cranking amps, we all know it well here. It's a big heavy beast.

Expecting that from something portable, lightweight or reliable isn't in my opinion reasonable. Sure, lithium can do it. But reliably and safely in a small package?

Jump packs exist to give the vehicle battery a boost. Connecting one up to a completely dead vehicle battery probably won't be that successful, firstly because you're dumping current straight into that dead battery.

Considering most of the cheap crap SLA ones have a single 10 or 14ah battery in them, I'd say 42ah or the 44 as mine has is pretty good. Also quite a bit bigger than you'll find on a moped I'm sure...

But none will be as good a match as decent jump leads, connected to a running vehicle supplying essentially endless current to charge the dead battery.

Well I was joking about a 'moped' Sloth (but they do use them in TOY sit-in cars) !

https://www.thebatteryshop.co.uk/lslc42-12-12v-42ah-cyclic-and-standby-battery-5124-p.asp

("Battery Type: Standby and Cyclic battery
Design life : 3 - 5 Year design life when used in standby applications.
Commonly used in Alarm Systems, Emergency Lighting, Ride on Toys, Torches, UPS systems and other electrical systems")

When it is new and fully charged that £156 "Clarke Jump Start 4000" might be able to give a 'boost' as you say: Problem is folks generally tend to forget to recharge them, (even though you can do it via the cigarette lighter socket) then they also flatten completly and suffer as a result of that.... !
Lucas replacements are about £90 and you can get a much better/bigger battery for that to use with shortish jump leads on a P38 for example...
and it will work when the main battery is completely flat too

EDIT/CORRECTION: The Clarke 4000 has a 38Ah balttery; That 42Ah battery mentioned above is a replacement for it.....

Their video says 30Ah..... https://vimeo.com/185778226

They're also used extensively in electric wheelchairs.

Speaking of which, a friend of mine builds and maintains them - so conveniently I have a source of good quality lead acid batteries direct from his supplier. Lucas isn't on that list of decent batteries - given they just slap their name on someone else's battery of unknown quality.

Not keeping them charged is the user's problem so far as I'm concerned. It's like a torch.. a device used for storing dead batteries ;)

As for using a bigger battery - that's fine, but the bigger it is, the less convenient it ends up being. Always a trade off. I have a spare 88ah battery that kicks around being used and abused. Even in the back of the RR, it isn't s small or light thing to push to one side.

The answer is probably a larger lithium pack so your not booting its arse quite so hard. But as always its a balance between cost, size and what you can get away with.

Like the aforementioned 6mm jump leads, my mate had used them a few times to jump start cars, and they worked fine. Becuase in those situations it was just a helping hand. But trying to jump start a totally dead battery is a different task that they just werent up to.

They can be handy to have around, especially with a built in compressor / little invertor.
I prefer the type you can jump start from instantly rather than those that charge the car battery.
But types with sealed lead/acid batteries that you can jump start from instantly are usually in an over-sized housing and take up much more space than necessary. Built in extras like compressors are usually very low quality even by mini compressor standards and wear out very quickly.
Most with lead/acid batteries have their charge socket connected directly to the battery, so if you do leave plugged into a car cig lighter socket and the lighter socket isn't ignition switched, if anything flattens the car battery it will also flatten the jump start battery.

For a really good set of jump leads you're probably better off making your own from welding cable. The cost of copper to make a decent set of cables would be more than the full price of most cheap cables.