Battery backup for radio

[Spittybug]

It's hot in Houston and car batteries don't like that. Long stays in the garage and the battery runs down from the small drains. I therefore have a cutoff switch on my battery compartment door. I have an Alpine head unit that therefore loses its secondary power and 'forgets' its settings. I'm tired of having to reconfigure it so I thought I should just wire in a 12v backup just for it.

I haven't done it yet, but it seems straightforward enough. If I put a diode in the harness that feeds the radio with car 12v (on the always hot line), then I should be able to add my 12v backup on the radio side of that diode and be good to go, right? The diode will stop the new backup battery from backfeeding other drains like the door locks, yet give the radio the minor juice it needs to keep the memory alive. In a perfect world the battery backup would actually be a rechargeable setup so that when the main battery is turned on it would charge my backup.........

Sound right? Anyone done this?

[Bitsyncmaster]

You should have a separate feed wire on the radio for memory battery. That wire should not backfeed but a diode won't hurt and my reduce the current a little. So yes just add a one amp fused wire from the battery to that memory wire.

[DMCMW Dave]

Unless the radio memory is what's running down the battery.

[Spittybug]

You should have a separate feed wire on the radio for memory battery. That wire should not backfeed but a diode won't hurt and my reduce the current a little. So yes just add a one amp fused wire from the battery to that memory wire.

I want to make it so that the main battery still feeds the memory of the radio, but that a second smaller battery does ALSO for when the main is shut off. That's why I need the diode..... And Mr. Swingle, you may have a point; I should probably check the draw with and without the radio and see what the door locks are taking.

[Bitsyncmaster]

Unless the radio memory is what's running down the battery.

Of course you should check that drain. I think Ozzie had a faulty radio that would drain the battery. Your looking for less than one ma. to not drain much.

Stock door lock ECU was draining about 12 ma.
Stock clock was draining about 5 ma.

Those stock drains would kill your battery sitting for about two months. My Fan Zilla would also drain about 3 ma and the new radio I never checked the drain. I have a battery kill relay but only use it when I'm working on electrical circuits.

[iflights]

Of course you should check that drain. I think Ozzie had a faulty radio that would drain the battery. Your looking for less than one ma. to not drain much.

Stock door lock ECU was draining about 12 ma.
Stock clock was draining about 5 ma.

Those stock drains would kill your battery sitting for about two months. My Fan Zilla would also drain about 3 ma and the new radio I never checked the drain. I have a battery kill relay but only use it when I'm working on electrical circuits.

I have a draw of 25ma with doors closed & dome lights off, is that a realistic drain when the car is not in use?

[Bitsyncmaster]

I have a draw of 25ma with doors closed & dome lights off, is that a realistic drain when the car is not in use?

It's probably typical and would not hurt you with a daily driver but when your car sits for months without running, it's a problem.

[iflights]

It's probably typical and would not hurt you with a daily driver but when your car sits for months without running, it's a problem.

Thank you.