On Sunday, December 6, 2015 at 2:27:45 PM UTC, wrote:
The places with the best prices for MDF/ply sheets tend not to have
panel saws so I'm wondering about getting a cheap cordless saw so I can
cut roughly to size in the car park and get the bits in the car. This is
likely to be the only use for it so required depth of cut is only 25mm,
and quality doesn't matter as long as it will do the job. 12V would be
good because then I could run it from the car if the battery died,
although something designed to run between 10.8V and 18V would probably
do the job well enough.
Any suggestions?

I'd push you towards a 14.4V cordless jigsaw.
Firstly vehicle electrics when the alternator is running are at 14.4V not 12V. This is not the main point.
You'd be better of charging the battery the using the tool rather than run it directly off the power power charger, but you could probably make up something with a lead and an old battery pack for the tool.
I'd recommend a jigsaw as far more versatile and much less likely to cause serious collateral/accidental damage to other things than a circular saw.

This advice is worth ignoring if you so desire.

E