Graig Writes:
"I have a TSIO 550 with a 24v system and I am investigating using two 12v / 17amp hr batteries in series.  The battery I'm looking at is the BB Battery Company model BP17-12."

I have been using a similar setup using two 20 AH Panasonic batteries LC-X1220P for 13 years. I just installed my 4th set and have always replaced on time rather than on performance. I have never had battery problems. The original set spent two years in the plane then served another 9 years in my lab powering various projects until I overcharged and killed one of the cells.  I have never used the BB brand and I suspect they are a China clone.  I would suggest spending the extra 10 gallons of gas for the Panasonics, more watt hours per pound. Back when we were participating in Battlebots I did some drop tests on the Panasonic batteries. With only 1/2" of  high density foam padding the battery was able to survive a 1,000 G shock.

In the airplane, because there is no free liquid electrolyte I was able to mount the batteries flush to the firewall (14 degrees off of vertical), saving a little space. The battery box is carbon fiber with a 6 bid E-glass top cover and a thermal protection blanket (Zetex 600A). The firewall is the back wall of the battery box, saving weight. The relays are mounted on phenolic blocks.

The only tricky part is are the battery terminals. Since they are Pb and will deform with time and vibration I  made some square washers out of brass to maximize the clamped surface area. I also used brass straps to connect the two batteries together. Finally, I machined some brass bar stock so that one end accepted the battery cable conductor and the other was a threaded stud (10-32 thread). This was soldered onto the end of the cable and the stud passed through one of the square washers, the battery post, another washer and then a nut.

Finally, remember to always disconnect the battery ground first and reconnect the ground last.  This will minimize the opportunity to short (and vaporize) something valuable.  I learned this lesson after copper plating my thumb and getting a nasty flash burn.

Regards
Brent Regan