CGT Lags to Eco on Full Charge

Hey Guys,
I recently sold a Evolve CGT, and the new owner reported problems that night. The board tested fine on a ~8 mile ride, prior to sale, paired with a R2 remote. The buyer chose to purchase with the GT/R1 remote (which had not been used for ~1 year). After questionable pairing and on/off order, the board is now lagging from gt (or fast), to eco, on a full charge. The battery recovers indicated charge percentage normally, and "tops up"/ charges normally, but still continually drops to eco from both "GT" and "fast" modes, while fully charged as soon as a full acceleration is demanded. Remote & board have been re-paired, multiple times, with no improvement. Board is ~3 years old with less than 40 charges, and is in 100% stock AT config. Any ideas idea on the problem/solution?

 

I think the battery pack is most likely worn out, due to age and possibly the way it was stored. Batteries do degrade over time, even if not used.