Battery charging

Hi,

hit some weird problem and not sure where to start.

I built a new battery box for the SLA battery. This is my 4th, but first one I'm having problem with.

When I try to charge battery in the box charger either shows 100% charged or resets, starts charging from 0% and when it stops it's not fully charged (it's about 60% charged). When I  charge the same battery directly - it all goes fine.  I.e. it shows, say, 68% and charges up to 100%
Multimeter shows the same/similar reading (i.e. 12.4V when battery is at 68%)
There is no problem using battery after it is charged.

Battery box uses AWG 14 cable with inline fuse. I have two chargers / maintainers (different brands), and both behave the same. Never noticed anything like this with previous boxes.

Any idea? I'm about to start believing in magic again.

 
  Quick thought, maybe slight resistance in the wiring?  Are the connections crimped or soldered?

2 cramped / 4 soldered.

I guess I'll just have to re-do it all completely eventually