[Elecraft] K2 battery options

[Louandzip]

I'm looking at current options for K2 battery operation.  I built mine 20 years ago and never got the internal SLA option. I always used an external battery.  I see the KBAT2 is still available but wonder about some of the newer battery types; Li-Ion, LiFePO4 etc.  I saw LiPO conversion from '04 that fit in the internal SLA holder, but I'm not enthused about that.  Internal is nice, but not essential.  What are you using and recommending?
Lou W7HV