Powering Circuit Question combining lead acid and d battery

[lloydi12345]

Hi, I would like to ask if the setup I made below is fine. Is it okay to have one 6v lead acid battery at the top and one 1.5v D battery below? What's the first one to be drained? Is it the 6v SLA battery or the D battery? I am using this setup since using two 6v SLA takes a lot of space. Thank you in advance.

Regards,

lloydi12345

 

[ericgibbs]

hi,
Its never a good idea to use series batteries that have different internal chemistry, if the 'D' becomes exhausted the and the SLA is still OK it will try to drive reverse current thru the D cell.

 

[lloydi12345]

thanks for that ericgibbs.

 

[MikeMl]

If you really, really want to get 8V out of a 6V SLA, use a step-up switching converter.

 

[lloydi12345]

Hi MikeMl, I can't see any setup about this

 

[blueroomelectronics]

Why not use several D cells instead.