Bike charger/optimiser on a car?

[Joe M]

Any reason why I cant use a bike battery optimiser to keep my M3 topped up when its in the garage for extended periods? Both 12V batteries and its not like im using it to charge up from drained.
If them low output solar charges can do it I would have thought the bike one is ideal?

Sold all my bikes btw, so have an optimiser gathering dust I can use.

[trickywoo]

I don't know about other makes but an Optimate is only rated at 35Ah. Most car batteries are going to be a lot higher than that.

I recently tried an Optimate on a 88Ah battery and after 10 hours it was still only charging at 12.8 V.

It would probably work just as a top up charger on a car battery but I wouldn't expect it to recover a flat one like it might with a bike sized battery.

[Joe M]

Yeah, its only for topping up. 35Ah should be fine for this, as long as its higher than the drain on the battery (which will be very low in storage) then it will keep it topped up?

[Mr2Mike]

trickywoo said:

I don't know about other makes but an Optimate is only rated at 35Ah. Most car batteries are going to be a lot higher than that.

The battery capacity makes no difference for maintenance duty, it just means it would take a ridiculously long time to actually charge the battery from flat.

[Locknut]

trickywoo said:

I recently tried an Optimate on a 88Ah battery and after 10 hours it was still only charging at 12.8 V.

There's something wrong there, a battery will not charge at 12.8v and if that's what your charger was putting out then you have a faulty charger. As Mr2Mike has said, capacity has nothing to do with it.

Are we talking about those chargers which pulse the current to keep the battery in good condition? If so, they gradually build the voltage up to 14.4v and stop charging. If the voltage decays to 12.9v they start a new cycle and build the voltage up to 14.4v again. Could your charger have been at the end of a cycle when you got that reading?

In answer to the original query: yes a 12v bike charger will maintain your car battery.

[nick_968]

I use my Optimate on car batteries all the time, works fine. Takes 2 or 3 days to charge a large car battery from flat, less to top up.

[rsv gone!]

nick_968 said:

I use my Optimate on car batteries all the time, works fine. Takes 2 or 3 days to charge a large car battery from flat, less to top up.

I had cause to use one on a car. As above, it took about 48 hrs but it got there in the end (until the battery finally failed).

Incidentally, you need to read the instructions. My Optimate 4 only stays in 'charge' mode for a certain time, which was insufficient for the car. You need to unplug and re-plug in the charger to reset it.