Starting a car with flat battery

[codek]

Hi,

Having woes with a flat battery, deemed "servicable" by the RAC.

I spotted these on ebay, they seem too good to be true. Seriously 13-15 jumps from one charge? Do they work?

https://www.ebay.co.uk/itm/12000mAh-Car-Jump-Start...

Dan

[Speed addicted]

Just buy a new battery? If the one in the car is ok but not charging you need to find out why it's not charging or what is draining it.

[Baldchap]

I have a similar device that seems to work well, though it isn't that specific one.

[InitialDave]

If it's a one-off situation to get the car started, just jump it from another car, then try a battery conditioning charger to see if it can improve matters.

But if it's happened a couple of times, and there's no obvious excessive power drain when the car's parked up, I'd usually say just replace the battery and be done with it.

[Chrismawa]

I have one of these from Halfords, seems a better solution than jump leads. Also provides a few othe ruses.

I haven't used it yet though, so this is probably a pointless post tbh

[Denis O]

Those battery tenders are excellent. Small and powerful.

I have a 20ft power boat with a single battery and once the auto bilge pump gets running due to rain it doesn't take long to use the battery power, i.e. no power for starting so I bought a Flureon branded tender and it's never let me down. That's starting a 3.0 litre petrol engine although the advertising blurb suggests it'll start a 3.0 litre oil burner.

Highly recommend these for lightness and power. Just keep it charged.

[catso]

codek said:

I spotted these on ebay, they seem too good to be true. Seriously 13-15 jumps from one charge? Do they work?

I've got one that's very similar and it has easily started a couple of different cars although both small engined, so can't vouch for the '4.0 diesel' claim or whether you'd get 15 starts from a charge.

Certainly beats messing about with jump leads though.

[Norse_mann]

I've got a similar one (might have a higher power rating) and I use it occasionally to start various decrepit diesel landrovers and it seems to cope with them.

[Penelope Stopit]

Read whats written on the tin

500 Amps no way

Those jump cables don't look like they'll carry 100 Amps

The Internet is full of.........................

The thing is, if they work they work but........

[milkround]

Penelope Stopit said:

Read whats written on the tin

500 Amps no way

Those jump cables don't look like they'll carry 100 Amps

The Internet is full of.........................

The thing is, if they work they work but........

This. If those cables tried carrying 500A the plastic would be melting before you had turned the key and carnage would begin.

This sort of kit does work though. I have seen not much more tougher looking versions start trucks. In fact it's a pretty smart thing to keep in the cab if you sleep out. If you run the battery down boiling the kettle or charging the laptop you can easily get it going without making a fool of yourself and having to call out a fitter and absorbing abuse from your boss.

[Riley Blue]

I have one of these: https://www.ebay.co.uk/itm/Suaoki-U28-2000A-Car-Ba...

It has never failed to start any of my cars when needed, from 1.5 to 4.2 litres.

[GreenV8S]

milkround said:

it's a pretty smart thing to keep in the cab if you sleep out. If you run the battery down boiling the kettle or charging the laptop

Would it not be cheaper and safer to use a separate lead acid battery to power that sort of thing? It would also avoid the risk of deep discharging the main battery - which is bad for it.

[Julian Thompson]

Very short cables = very much less resistance

= don’t need as big a cable to carry a given current....

[GreenV8S]

Julian Thompson said:

Very short cables = very much less resistance

= don’t need as big a cable to carry a given current....

Not quite right. The cable section determines the resistance and heat per length. A cable that is too small for the current will overheat regardless of how short it is. The length just determines the overall voltage drop.

[milkround]

GreenV8S said:

Would it not be cheaper and safer to use a separate lead acid battery to power that sort of thing? It would also avoid the risk of deep discharging the main battery - which is bad for it.

Well many firms who will want you to sleep out fit an inverter and wouldn't be impressed with you bringing your own batteries along. Plus they are heavy. What's more - they would need to recharge them regularly. Most firms wouldn't be happy with you wiring up your battery when driving etc. And if you left it connected all the time it would run the 'truck' one down at the same time.

Technically most trucks have overcharge protection now. But it can be turned off. Sainsburys are a pain for this. They buy their trucks outright and their fitters will turn it off when drivers whinge rather than change the batteries (if it kicks in you can end up stranded in a trailer with no lights or safe way to get down). And then they complain when you need a fitter to come out who changes the batteries at an extreme cost. You don't sleep out with them - but the unit might be running all the lights in the fridge and the taillift etc - and they do a lot of stop start so the batteries take a beating. Penny rich pound smart comes to mind.

You will see a lot of drivers from Europe running the engine when weekending in the services when they make their dinner to stop this being a problem. But we are well off topic now. Personally I carry a 'truck' version of this and jump start it unless I'm driving for a huge firm who would rather you call out a fitter.

[paintman]

codek said:

Hi,

Having woes with a flat battery, deemed "servicable" by the RAC.

Dan

Fully charge the battery with a battery charger & see what happens - as in does it hold the charge or not.
If not it could be a defective battery - how old is it? - or lots of short journeys or a parasitic battery drain or a faulty alternator.

[rxe]

GreenV8S said:

Not quite right. The cable section determines the resistance and heat per length. A cable that is too small for the current will overheat regardless of how short it is. The length just determines the overall voltage drop.

Of course, but it is a sliding scale of voltage drop.

Those leads will pass 500A for a few seconds easily, They're 8 gauge or so - about 0.02 ohms per metre. A metre set of leads give you a voltage drop of 10V passing 500A. A 10 cm set of leads will have a 2V drop, so 10V at the starter, and this will work fine. In terms of heat, it will lose a kW, which is fine for a few seconds - but that is about as long as the battery will last anyway.

These things work remarkably well. I've started a 4.6 litre V8 loads of times with one.

[Julian Thompson]

GreenV8S said:

Julian Thompson said:

Very short cables = very much less resistance

= don’t need as big a cable to carry a given current....

Not quite right. The cable section determines the resistance and heat per length. A cable that is too small for the current will overheat regardless of how short it is. The length just determines the overall voltage drop.

... so with less volts because of the higher resistance you get more amps! And around we go!

Therefore, a shorter cable means that you don’t need the same cross sectional area as you do if you use a longer cable!

[GreenV8S]

Julian Thompson said:

... so with less volts because of the higher resistance you get more amps!

You want to run that past me one more time?

[Penelope Stopit]

Penelope Stopit said:

Penelope Stopit said:

Read whats written on the tin

500 Amps no way

Those jump cables don't look like they'll carry 100 Amps

The Internet is full of.........................

The thing is, if they work they work but........

Excuse the pun

What have I started?

Penelope Stopit said:

Julian Thompson said:

Therefore, a shorter cable means that you don’t need the same cross sectional area as you do if you use a longer cable

This is correct, the further you go the more the volt-drop increases. The higher the volt-drop, the hotter the cables

Penelope Stopit said:

Julian Thompson said:

Very short cables = very much less resistance

= don’t need as big a cable to carry a given current....

This is correct

Penelope Stopit said:

The problem with the Internet is that it's difficult to know who knows and who doesn't know, if you know what I mean like