Are you sure it's the batteries? My truck started smelling real bad on the interior and it turned out that there was mold accumulating on the heater core. I had it in for routine maint. and I asked the dealer about this. They said while they were replacing my cabin filters they would spray some mold killer (?) on the core. Two years later no smell. ALSO, I always turn off the A/C and let the blower run for a few minutes before I shut the truck down. Apparently moisture accumulates on the core while in the A/C mode and then gets moldy. Turning on the heat speeds up the process. I may be off target here, but that fixed my smelly problem. Good luck.
JP
Jeff
"But officer, I ain't Speedin', I'm just flyin' low"
2001 Silverado 3500 Dually LS Ext Cab, 6.6L Diesel, Banks Stinger Kit, 4" Exhaust, VR Straps, Bilstein shocks, 255/85/16 BFG KM2s
2004 Suburban 2500 LT 6.0L 4x4, Bilstein Shocks, Federico front/rear sway bars
1996 Caprice 5.7L LT1, B4U Suspension, KYB shocks & Hotchkis sway bars, BMR RCA - alas I miss ya.
2013 Caprice PPV 6.0L