How do you top up charge a motorcycle battery from a car?

My battery failed this morning and I checked and found it was running at 10.0 volts. All I get is the starter engine gunning out.

Does anyone know how to top up the bike battery from a car using jump leads? Because the car battery voltage is greater, I guess I can’t do this directly without damaging something.

Can anyone tell me how to top-up charge my bike battery safely using car jump leads?



For starting you just use a decent pair of jump leads like any other jump start*, except: Be very careful, bike batteries are mostly a tight fit in the frame and it’s very important that the lead clips are not touching the frame or any other metal.

(* That’s + to +, - to -. For the technical, in parallel.)

For sort of recharging, with both ignition circuits off, connect as for a jump start and leave for half an hour. When you come back you’ll have two flat batteries and be screwed, but hey, you tried.

For re charging, you can do the same with the car engine running but the bike ignition off, and then wander off for a cup of tea. When you come back you’ll probably find some toe rag has stolen your car. But the bike might start.

Do u think this will work for my battery? It isn’t deep discharged. So For this method, I have to have the car engine running while I jump start on the bike?

Is it okay to start the car and leave it idling and then jump start the bike? My battery is under my seat. Limited way to start it not sitting on the bike.

The other ways you described don’t sound great :frowning:

You shouldnt need the car running to jump the bike, once the bikes running give it a run. You could load it up put main beam on and indicators that sort of thing and leave to idle but i shouldnt imagine it’ll give it much…

This cold weather does for battery’s if your not on top of them.

An Optimate is a good investment if the bike sits for any length of time, keeps the battery alive…best of luck chap.

I don’t understand. Do you mean if I connect the car battery in parallel with my flat motorcycle battery without starting the engine, the voltage potential will trickle enough to the motorcycle battery to restart it, without starting the car engine?

It’s late and I’m tired after taking public transport and queuing all day. I’ll try and face it tomorrow.

Thanks for helping.


Good words! … use an Optimate/optimiser, they’re excellent. But realise a jump start is different, and if you jumpstart your bike every day, it will kill the battery anyway. Batteries don’t cope well with that kind of hammering, but if you keep them topped up … they can last ages.

A jump start is a the parallel connection of the two batteries. It will start your bike, but don’t do it all the time.

By ‘jump start’, he means attach the jump leads then hit the starter button, should be perfectly doable with the seat off.

You basically use the car’s charging circuit to charge the bike’s battery and power the starter motor, and once the bike’s engine’s going it’ll take care of itself, just do a reasonable-ish length ride to get some charge into the battery.

You’d get some movement without the car running, 'cause the charged battery in the car will be at ~13V which is higher than the bikes 10V. But you’d likely just end up with the bike one less flat but still useless, and the car one uselessly flat also.

It’s worth looking into why the bike battery’s flat, too.

The charging wires aren’t long enough!

No matter what position I move my bike, I can’t get right without blocking traffic :frowning:

Optimate it is then…

Thanks for all the suggestions.

car and bike batteries are same voltage but car battery is bigger ampere.

Sorry if I caused confusion. I was just pointing out that there are option but some have down sides.

I agree with all that has been said. Using jump leads once in a while when you’ve cocked up and left your lights on, or whatever, is fine. If you need to do it regularly the battery is knackered and the only sure fix is a new one.

If everything is good and you are doing, say, 5+ miles after every start, you should not need to use an Optimate (or similar) unless the battery is a few years old or the air temperature is below zero for a day or two and the bikes been sitting idle.

Well, there are a few problems with constant current drain from alarms/immobilisers. If you have one of those, buy a new battery AND an Optimate.

Fair makes me wistfull for the days of bikes having kick starts. Well, almost.

O.K. they were cwap and so were most of the bikes that came with them. Give me a decent battery and a push button starter any day.

It’s always worth getting one of those jump start packs circa £30. That do do a car or a bike. Some have a air compressor in to pump up your tyres as well.

The starter packs have a on/off switch to only switch on the power when your connections are sound. With a direct jump between the car and the bike you are in danger of getting a big fat juicy spark as you connect the clips, Which has been known to fry an ECU.

Good point about the current spike/ECU’s on connection with a jump start. Should have remembered as a garage owning friend has just bought a Peugeot with a fried ECU for his new driver daughter. £675 for a new ECU from the makers so true bonus price for the non running car.

(£150 if you’re in the trade and know where to go for a re build. Is re build the right word for solid state stuff?)

Anyway, asked what you can do to avoid the spike and he told me his emergency start unit has “soft start”. Takes about 2 seconds from flicking the switch to full power but it is spikeless. Down side. £lots. But cheaper than a new ECU at £150.

You can buy several batteries and an Optimate for that money.

Bite the bullet. Got buy a new battery before winter comes on properly.

Once you’re started hte bike batt should charge itself back up but to do so you need a good run at higher than city commuting revs… ie several thou rpm of a half hour motorway run, not the stop start nonsense of traffic clattering. If you’re batt’s not holding charge, get yourself a proper trickle charger with analysis capability and it’ll tell you if the batt’s the problem or whether you need to look elsewhere…