2yrold interstate bat dies

last time I mowed with my 950 I noticed the (non oem ) volt meter showing low like 8-10v.. thought my vreg or genny was going bad

12v gen off a diesel 4 cyl,and a 78dt megatron interstate bat.

I jimmied the reg with a tickle wire to get V up a lil and finished mowing.

went to start the other day and bat dead.. I figured ok.. vreg was gone and let her run down mowing last time..

charged bat up on a 2a trickle all day.. the topped with a 10a noticed needle swinging ont he 10a charger as it's cktbrkr was opening..

checked bat. 8v

let it set and it dropped to 6.3 within 20 m... and never went lower. tried it on the 80a charger at work and it just gassed and boiled alot.. but still 6v.

wow.. I've lose a cell or 2 in a bat before.. but never 3 cells.

and bat ain't even old really..!

swapped in my spare DT battery fired up and mowed this am..