B battery (vacuum tubes)

In electronics, a B battery is any dry battery" (although there's no reason why a "wet" battery of suitable voltage couldn't be utilised for the purpose) The term comes from the days of valve (tube) radios when it was common practice to use a dry battery for the plate (Anode) voltage and a rechargeable lead/acid "wet" battery for the filament voltage. The A Battery serves primarily as a heat source and rapidly discharges, while the B battery experiences very little current draw and retains its stored capacity far longer than an A Battery.