Hello,

There are two 12 volt lines.
One positive and one negative.
What diode is D5 next to the transistor?

Bertus

 

Hello,

There are two 12 volt lines.
One positive and one negative.
What diode is D5 next to the transistor?

Bertus

It is a 149.

 

Ni chemistry cells are tricky to charge properly. Many devices don't even try and just trickle charge them. SLA are dirt cheap and easy to charge correctly with just current and voltage limiting. Lithium-ion likewise, since there's oodles of charger chips and modules available off-the-shelf. LiFePO4 is generally safer than lithium-ion; 4S is a near perfect voltage match to 12V SLA, and there's also plenty of charger options. You can get protected LiFe batteries in packages the same dimensions as common SLA batteries. They're not as cheap, but should last a very long time.