Caveat: The following battery is only available in standard BCI sizes of 24, 27, 31, 4D, 8D
CROWN BATTERY
NAME OF SERIES: Severe Duty
The charging needs of this type of construction closely mimics that of AGM batteries. Voltage specs for both absorbsion and storage (float) are identical. Self-discharge at all temps mimics that for AGM
The battery is of calcium/calcium construction so it needs almost no watering.
Calcium calcium makes for a horrible cyclable battery so just to caution you.
Crown enjoys a top drawer reputation for their cyclable batteries so this series may be of interest.
Price and availability are unknown to me. But when my unit calls for replacements (2) I'll take a closer look.
http://www.crownbattery.com/find-a-distributor
