I have made a very simple battery backup for my garage door: 2 x 12 V batteries in series connected to the battery terminals of my opener.

This charges the battery and switches to backup on power failure.

My question is: before I build a second backup for my other door, can I simply wire both doors into this one backup? I am concerned with having two door openers charging the batteries at the same time.

I was considering having an DPDT switch so the one backup can open both doors but I have to manually switch between them.

But if there are no issues wiring them together it would be best option.

  • \$\begingroup\$ It all depends on how intelligent the charging circuits are. To know that requires knowing the circuitry at the very least so, please supply a schematic circuit diagram. If you can't then how can you get an answer? \$\endgroup\$
    – Andy aka
    Apr 9, 2020 at 13:31
  • \$\begingroup\$ Hi thanks for the reply. I am a very novice DIYer. It is a Liftmaster LM 80evs and sorry I cannot find out anything about how the device charges the backup battery. I have tested and it is not putting 24v from the device to charge the batteries. Sorry \$\endgroup\$
    – Gary Weir
    Apr 10, 2020 at 12:25

1 Answer 1


Block both positive lines from charging the battery, use a diode, and put a tricycle charger on the battery separately.

That's what I would do.


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