I agree Alain. I usually think on terms of reliable commercial product, that is well in the middle of the specs.

It can work with little tricks and magic, but I won't trust it. Especially with the lead batteries!

On the other hand the idea of the linear power supply is so simple... And prooved reliable.

The Pic will only have to create the Vref and then a comparator will adjust the base voltage of the pass transistor. Thats it!

Ioannis