nice to see this thread,here's what I did a couple of months ago.
I have a couple of Hensel Porty Premiums with the bigger lead acid batteries.
I am in the UK and sourced the same battery only LI+, very inexpensive compared to buying new lighter ones from Hensel.
everything was easy to do and they work fine, my problem however is two fold, hopefully some bright sparks on here can help.
firstly I cannot run these new lighter batteries at full power... it just shuts the whole thing down, anything up to one stop below full power and it's fine.
Second niggle is that I cannot run these batteries on the faster recycle mode, again it just shuts them down, it's not a huge problem as they recycle quicker than the older sealed ones.
I suspect that these batteries are maybe not as powerful as they say on the box so to speak, but any thoughts from fellow readers would be welcome.