Flat batteries

I had 2 oximiser trickle chargers one on a V7 and one on aV50 Over the winter during March a visiting electrician switched off the shed power for a week - this seemed to do in both batteries which will only hold 10.8v after 24 hrs. I put a spare battery (Off a Honda 250)
The spec was a bit low for the V7 but it started it 3 times with no effort and was reading 12.6v with engine off - So I went fora spin 15 mins down the road and the battery is flat and engine cuts out. Has the 2 optimisers (with no power on) Caused a problem by battery power feeding back from 1 bike to another or is it a coincidence and it
Needs regulated etc checking out, or would the small battery just be too small to power headlight and fueling electrics? (the Honda has fuel injection and lights on)?

Batteries should survive being left for a week. How old are they? 4 to 5 years is the typical life span of a lead acid battery.
My bikes are older and don’t have the drain of the V7 but the V50 should be fine if left for ages.
The Honda battery should have been fine so long as the connections were tight and clean. The only need for a decent battery is for starting. I would check your charging system. Put an analogue voltmeter acros the battery with the engine running. It should go up to around 14V at 3000 rpm. Don’t use a digital guage, they can’t keep up with the fluctuations.

I think the charger lights still connected to the batteries caused the initial discharge one battery was over 3 years old the V50 battery was newer but a cheapey so maybe they were on there way out.as for the breakdown I’ll do as you suggest And check the charging.

If you have one, it would be worthwhile trying to charge the old batteries with an old style battery charger that just pumps power into the batterry, that will sometimes rejuvinate a battery from being totally flat when an optimate just says No.

March 23rd I parked up Breva and removed the negative cable from the battery. 30th May I removed the battery and installed it in my Nevada which had been stood since 30th Oct 19. The Nevada fired up like it had been run the day before. No chargers were used in these activities.