I've had very good luck using the lithium ion and polymer in my X2 transmitters, I bought 2 of each so far get great life out of them. I'll definitely save $ and be a little more environmentally friendly over time. I think one key is to use them til they die, having 2 complete X2 rigs helps because I always have a spare ready to go.
P5, 5/1, SKB 3005, VM P5, CS '59 NOS P, Fender JPJ, Antigua P
CMD 102P + 102HF, LMII + Thunderchild 115 Composite
X2, TU2, Fodera 2000, Bassbone, Compressore, Fdeck, Pedaltrain