FLA battery top-up

[Nickel2]

I have had my 'Nickel-wall' batteries for 6 months now, and I need some definitive advice on battery maintenance please!
They are four 200Ah 12v each, arranged 2S-2P to give 24V 400 Ah. (nominally 10kWh). All are about 4 years old,  so getting tired.
As they were originally big generator (2MW) starter-batteries. I do not deep cycle them, but use a maximum of 10% of the available capacity, i.e. less than 1 kWh per charge/discharge cycle.
The electrolyte level is the same in each cell, and I have recently topped them up using deionised water from halfrauds. (£3-ish per 5l pot).
They take 200 cc per cell to raise the electrolyte level by 10 mm. The plates are still covered by 20 mm, but the level is still below the minimum marker on the cases.
Now the questions:
How much juice do I put in at a time?
Do I add after or before charging?
Do I run the battery low before top-up?
Please steer me in the right direction, I know they are old, but I'd like to eke 'em out for as long as possible, due to 'funding issues'.
Do I need to buy a cheap hydrometer?
Cheers all!
 

[camillitech]

Top them up when required to the correct level. If you are an anorak like me, check them regularly and take and record SG readings before topping up. You get to know your batteries as to when to do it, me, I know at what level I can suck the electrolyte before it gets too low. If they have gottten too low to suck up the acid I top up first, run an EQ then record.



As for hydrometers, I have spent 20 years looking after numerous FLA banks on ships using hydromters of all descriptions from £3 ones to £300 ones and to be quite honest there aint much in it, none of them are worth a toss. My £50 Durite is no better thaN the £5 Draper, in fact the cheapo is at least acid proof. The important thing is that you always use the same one.

[Scruff]

All are about 4 years old,  so getting tired.

Where's the evidence..comparative li-ion studies was it? Mine are 5yo, last discharge tested 3 weeks ago at 100% rated.

How much juice do I put in at a time?

I like to overfill it increases the watering interval.

Do I add after or before charging?

After electrolyte expands as the battery is charged

Do I run the battery low before top-up?

Not unless you want to.

Please steer me in the right direction, I know they are old, but I'd like top eke 'em out for as long as possible, due to 'funding issues'.

Hydrocaps.

Do I need to buy a cheap hydrometer?

Yes. How else are you supposed to tell if they are charged or not?
A graduated float one not an automotive floaty ball trinket.

[Scruff]

to be quite honest there aint much in it, none of them are worth a toss. My £50 Durite is no better thaN the £5 Draper, in fact the cheapo is at least acid proof. The important thing is that you always use the same one.

Agree, I have an extreme dislike of both those brands all the same durshyte and blue draper make everything as cheaply as possible, they don't last phishing time. Durshyte is usually over-rated, draper usually falls apart...the only tool I have made by draper that hasn't failed prematurely is my insulated crimp tool...well she's on the way out now defo...

I recommend a hydrometer with a plastic case because I usually break them.