[mxmtech]

I suppose I haven't really combined the batteries since they are on a double pole double throw switch. It is really two separate power sources.
I am using SLA's and Nicads. The SLA pack is 24 volt 12 AH and the Nicad is 24 volt 8 AH.
This morning it is 1 degree Celsius or 34 degrees Fahrenheit and there is the first snow of the year on the ground.
I began my morning trip using my old SLA pack that is probably down to about 6 AH. I haven't tested it yet (I'd like to put the batteries on my good charger and run the de-sulfator a bit)
In the summer I had been getting about 8 kilometers out of this pack but this morning I only got 3. So I flipped the switch and used the Nicad pack for the remaining 1 k.
Yesterday I needed to do some running around for parts and tools. I had my good SLA pack and the Nicad. I tried to use the Nicad as much as possible. The first thing that I noticed is that it produces noticably less punch than the SLA when going uphill. So I used the SLA for all the uphill portions of the 11 kilometer round trip.
I was really pleased that I was able to use the Nicad for the majority of the way and I did not run out of juice in that battery although it must have been pretty close. The SLA was still fresh.
The reason for the power difference is the size of the packs. 8 AH pack at 3C is 24 amps and 12 AH pack at 3C is 36 amps.

[mxmtech]

The SLA took a charge very quickly so that tells me that the battery isn't really discharged when I lose power, it is just that the cold weather is slowing the chemical processes inside the battery to the point that it is unusable.
The Nicad on the other hand completed my 4 kilometer trip to work with hardly any discernable loss of power.
No problem with the snow (less than 1/2 inch), but I'll have to put the studded ice tires on this weekend. The snow is gone now, turned to rain this afternoon.

PS:
3C means dead battery within 20 minutes regardless of what size battery pack or what battery chemistry. For those who don't know.