another battery question

[BALDY3260]

evening all, and happy new year. been having a few battery probs lately and looking for some advise. for the last 4-5 months i have been going to use the camper (westy/jx ) and found the starter battery flat, thought it might be the cold weather / lack of use so have jump started it and taken it for a good run, its then been fine for a couple of weeks, then same issue, go to use it and flat battery. so had the same problem just before xmas and have just got round to looking at it today, jump started it went for a 30 mile run out came home put it on charge, took 8 hrs for charger to show full (lidl type, recommended on here) however, when i checked voltage on battery after removing charger volts read 12.69. is this battery kerfurtled ? i only use the camper once a week to keep everything ticking over 20 mile round trip to work and back obviously it gets used more in the better weather and longer trips, is this a cause of the problem ? also just checking a few things whilst engine lid was open and found 11.69 volts between battery leads when disconnected from the battery does this indicate that the split charge relay has gone kerfluey ? i have radio and interior light mod to run them from the leisure and am now thinking that this relay maybe linking both batts together and draining the starter batt. can any one throw some light on this please regards baldy

[BALDY3260]

UPDATE
this morning, i checked battery voltage (left disconnected overnight) it has dropped to 12.39volts, so overnight it has lost 3volts. is this acceptable ? alternator output when engine running is 14.27 volts so i'm guessing that is ok.
all help greatly appreciated.
also starter battery is 480cca, and from reading other posts it seems it maybe a bit small for a diesel, so may change anyway for a bigger one. so the voltage at battery leads when disconnected from battery must be coming fron leisure battery through the split charge relay, any ideas what the relay is and where its available from regards baldy

[kevtherev]

Bad news then.. your battery is useless

If it drops below 12.6 that's it

good news is your charging system is top hole

[Red Westie]

Debating about the battery is immaterial as it needs replacing anyway.

Diesel minimum cold cranking amps need to be 680.

72 amp/hour 680CCA or higher for Diesel engines.

Diesel engine starters draw such high amps from cold..... probably the reason why the engine has killed the weak battery.
Martin