Bit of help needed with my maths

[Bonnox]

Hi guys just needing a bit of help, I'm in the process of building my off grid shed, I'm going to be using PVC panels and deep cycle batteries but currently can't afford the control unit to switch off the solar charging and not over charge the battery, and probably won't be able to till after Christmas now, so was going to use the two batteries I have and use one while one is charging and swap them around, just need the help with the maths to make sure I don't over charge them, and I'm not massively up on my technology and current conversion etc so.....

If I use for example a 75Ah battery I can use something that uses up 1 amp per hour for 75 hours,
And if the solar panel puts out/charges at 2Ah then it would take 37.5 hours to charge from flat till full, am I right in this ?

Many thanks for your guys help

[Lightspeed]

[Bonnox]

[Nix]

[Bonnox]

Yeah cheers guys I don't intend to ever let it run down to empty, I was just using the example to make the maths simpler to write up, Im led believe the same applies for charging batteries as well, that if they aren't fully topped up they have 'memory' so the full capacity of the battery can be lessened say if you only charge it to 70% each time then the battery thinks that 70% is actually full so 70% becomes the new 100% as it were! or is this only for the smaller batteries ?

[Nix]

Lead acid batteries, which includes the ultra deep cycle batteries, do not have a memory. I believe it's only the NiCd and NiMH rechargables that have this memory effect.

[Skvez]

As Nix says Lead Acid batteries do not have a (noticeable) memory effect.
As a battery approaches begin fully charged a larger percentage of the power you provide to charge it goes into heat.

If you have a 75Ah battery and discharge it to 2/3 full (50Ah) it can take noticeably longer than 25 hours of charging at 1A to fully charge it again.
Efficiency and losses.