The worst computer in the world for having a supposedly user
exchangable battery must be the Buddy Nexus.  It has a battery
compartment cover which is not retained by itself against its
o-ring.  You have to poke your finger through the back part of
the case and hold the cover (which you then can't see) in place
while you screw the case down and fold the rubber strap into
position.  An awful, awful design.  I changed mine once
successfully, but the second time must've unseated the o-ring
while screwing the cover down.  I noticed the battery nearly
flat light come on while diving the next time, so checked at the
end of the weekend.  The battery compartment had flooded and the
battery exploded, cracking the lid.  It carried on working for a
whole weekend, which was nice, but I reckoned that I'd be going
through batteries like nobody's business if I carried on using
it like that.  I now have an Apeks Quantum which looks like a
doddle to change (which is one of the reasons I got it) though I
have yet to do it.

Had my Viper in for new battery in Spring at my local supplier as
they sold it to me & they charged £25.00.  Thought this was quite
reasonable. I would rather pay a bit more to have it done right & tested
than a DIY job which may cause damage if I had boobed when replacing
the old battery.