Thanks for the link to that whitepaper, very instructive and reassuring.
It appears that my relatively soft and clean "mountain water" (Hetch
Hetchy) should be no major problem for this one refill. I estimate that
the cells are still under 10% of their max allowed impurity for Calcium
(refilling ~5% with water containing 53 PPM Calcium). I did notice that
the pack seems a little "soft" (sagging deeper than before the watering)
but I think I remember that this is normal - due to the lower SG the
resistance of the cells is slightly higher. Before watering the
electrolyte is a little too concentrated, giving better performance -
but also more plate corrosion.
I did indeed remove electrolyte from the top of the overfilled cell with
a plastic syringe and deposited it in a bottle, clearly marked as
"Battery Acid" to avoid more dangerous mistakes. Now I just need to wait
and drive the car until the level has gone down enough from the
recommended 1/8" below the bottom of the vent well and at the next
watering interval (which is half year due to my sparingly charging, even
though I use the car almost every day) I should be able to put that
electrolyte back in and bring the level back (close to) to recommended

Note that I did drive the car immediately after the overfill event, but
since I had fully charged the pack before, that only meant that the
level was dropping. I did remove electrolyte before charging again.
Due to my removing electrolyte while the cell was not fully charged, I
might have removed too little and the level is probably still higher
than the other cells. Hopefully the slightly lower SG will cause it to
lose more water than the adjacent cells. We'll see.
I have added a little "dam" of baking soda around the fill hole of that
cell, so if it spills during the end of charging, it should get
Other cells are occasionally losing a bit electrolyte also, while the
fill level of all is correct and none should have an issue during
But that is why I have baking soda scattered over the tops to catch some
of the electrolyte leaking.
I am not sure why one battery remains sealed and clean, while another
one constantly weeps elecrolyte. Probably a mechanical issue that the
seal of some fill holes is not seated properly. I am using the ganged
caps that allow all 3 holes to be opened/closed together.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation
Email: Private:
Skype: cor_van_de_water Tel: +1 408 383 7626

-----Original Message-----
From: EV [] On Behalf Of Roger Stockton
via EV
Sent: Monday, August 11, 2014 12:05 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Flooded lead-acid ooopsie and how to correct best?

Cor van de Water wrote:

> I presume that you meant to say "unless it's very high in minerals"
> and luckily our water is the "softest" in the area. I grabbed the
> report from the city and saw that our tap water has on average only
> 71 PPM (Parts per Million) total dissolved solids, of which
> 53 PPM calcium carbonate
> 12 PPM sodium
> The average Ph is 8.4 but varies between 6.5 and 9.4 since the total
> dissolved solids can vary between almost 0 and 109 PPM.
> That does mean that there are some impurities added to the cells, but
> not a large amount and since the amount of tapwater was approx 5% of
> total fluid contents of the cell (my estimate) the total impurity
> is about 3-4 PPM added total dissolved solids.
> I am no battery engineer though, so I do not know how bad that is,
> please enlighten me. Or time will tell...

Here is a Trojan whitepaper describing max allowable PPM for various
impurities and the detrimental effects of each:


For your over-filled cell(s), I would just remove electrolyte from the
cell until the level is restored to normal.  If you don't, you are
likely to lose electrolyte during charge and use of the vehicle due to
leakage out of the cell caps.  Reserve this electrolyte and use it to
top the cell up to normal level at your regular watering interval until
it has all been added back to the cell.

If you haven't yet driven or charged, then the liquid at the top of the
cell is likely almost all just the water that you added, with relatively
little electrolyte mixed in (the lower SG water will 'float' on top of
the heavier SG electrolyte that was in the cell to start with).


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