Why Does Time to Recharge Battery Vary So Much ?

alternator

This winter I have stored my new car in the garage and used only my second car. Every 3 to 4 weeks I connect a battery maintainer to recharge the new car's battery.

Usually that takes about 6-8 hours, but once it only took 3 hours and once it hadn't recharged after 12 hours.

Is it possible that a less-than-firm ground connection could cause this difference? At the start the maintainer always lights up to show it is connected.

Mr_Shiftright

hard to say but if you are using a small inexpensive battery maintainer, these were never meant to charge up a fully discharged battery, so it's possible that if, say, during a particularly cold stretch, your battery charge goes well below its normal "mildly discharged" state, then this little guy might be struggling to keep up.

Also, battery maintainers, unlike battery chargers, do not charge at a constant rate.

texases

Why not just keep it hooked up? That's what a maintainer is good at.

Mr_Shiftright

That's what I think, too. Using a maintainer as a stand-alone charger isn't what it was built for.

alternator

The time it wouldn't charge, I repositioned the leads and got full charge within about 2 hours.

I don't like to leave an unwatched electrical device turned on if I can help it. I don't see any advantage in leaving it connected and turned on.

Thanks for replies.