Deep cycle batteries - please help me fix!

[steve.lorimer]

Hi folks

I'm currently on a trans-Africa expedition. At the moment I've got 3 x 110 Amp/hour batteries in my truck, and after a year on the road, they're getting a little tired (ie: after many quite severe discharges they are not holding charge too well, or at least I get that impression - perhaps I'm just using too much charge and need to just increase the total Amp/hours capacity in my truck.) I'm in Nairobi in Kenya at the moment, and can get some new leisure batteries here.

My questions are thus:

1. If I buy some new batteries is it ok to connect them in parallel with the old batteries to eke out what life is left in the old batteries, or will the old batteries damage the new batteries, and therefore should I replace the old batteries in their entirety?

2. Is there a way to tell how much life is left in the old batteries? Will a battery outlet be able to tell me this? At what point should I consider replacing the old batteries?

3. If it's ok to add the new batteries in parallel with the old batteries, should I get new batteries with the same Amp/hour rating as my old batteries, or is it ok to mix and match Amp/hour ratings?

Many thanks in advance for your help!

Regards
Steve

(details on our journey if you're interested: www.overafrica.org)