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Battery SG question


By madlabs, Section Storage
Posted on Thu Jul 02, 2009 at 02:59:31 PM MST
When is a particular battery type full?

Hi All,

Well, been of the grid for a couple of weeks now. I have a question about specific gravity in batteries. When one looks around at various SG tables, there is variation on what the SG is when full, from around 1.300 to 1.275. I know this depends on the details of the manufacturing of the battery.

So, if the highest gravity I see when I equalize is 1.275, is there an equation to calculate what gravity to expect at a particular charge? I'd like to know what reading equals 80%, 75% and 50%.

Thanks for all the help.
Battery SG question | 7 comments (7 topical)

Re: Battery SG question (3.00 / 0) (#1)
by bob g on Thu Jul 02, 2009 at 09:25:38 AM MST

best advise i can give you is to contact the battery manufacture for specific
details on your batteries.

most manufactures are very helpful in this regard, they want their batteries to
make it through warrantee. :)

talk to them about recommended charging regimes, what you are using to charge with,
charge rates, and most important how often and at what voltage to equalize at.

don't reinvent the wheel here, the manufacture truely knows best how to maintain their batteries. straying from their recommendation is done at your own risk.

bob g



Re: Battery SG question (3.00 / 0) (#3)
by madlabs on Thu Jul 02, 2009 at 11:03:45 AM MST

Tried this and got the runaround. The lady I spoke to had no idea even what SG was. She has promised to get hold of her tech and email me back, but I'm not holding my breath. The batteries are Energizer EGC2's.

Jonathan

[ Parent ]



Re: Battery SG question (3.00 / 0) (#4)
by bob g on Thu Jul 02, 2009 at 11:17:32 AM MST

be persistent :)

call her back and ask for "engineering"
if she tells you they have "tech support" but no engineering,
ask her who manufactures their batteries???

get that name, and call and ask for their engineering dept.

sooner or later you will get to the guy in the know

just hope it isn't east penn, they won't even give an amp/hour chart
at various rates.
i refuse to buy batteries from anybody that cannot provide me with access to
an engineering dept.

gotta wonder what they are hiding?

bob g

[ Parent ]



Re: Battery SG question (3.00 / 0) (#5)
by ghurd on Thu Jul 02, 2009 at 12:45:45 PM MST

Did you call Energizer or Sam's Club?  hehe

Naturally Sam's Club does not have a battery factory,
And Energizer does not make lead-acid batteries.

Energizer evidently rented their name to Sam's Club for some re-stickered lead-acid batteries.

My bet is they are made by Interstate or Trojan.

The last 'brand' Sam's club sold was made by Trojan and rolled off the same line with the same parts, different case color.

Might try calling her back and asking for the "MSDS" data sheets.
Many places do not bother to change the name at the top or in the bottom fine print copyright section, so it may say "Interstate" or "Trojan" or "somebody else" at the top/bottom.
Then cross your specs to their part number.
G-


[ Parent ]



Re: Battery SG question (3.00 / 0) (#2)
by Curbie on Thu Jul 02, 2009 at 10:44:52 AM MST

If your manufacture is not that helpful or just very busy try:

First determine the specific gravity range for your battery, and then you can create a rough chart to the relationship between voyage, specific gravity, and percent of discharge.

Say your manufacture considers a fully charged battery has a specific gravity of 1.275 and they consider a specific gravity of 1.150 to be fully discharged. If you subtract 1.150 from 1.275 you get partial charge range of 0.125. Divide this by 10 to get the 10% increment for the level of discharge based on the specific gravity of the electrolyte.

To roughly correlate the specific gravity to cell voyage use the following formula:
Specific gravity = open circuit voltage minus - 0.845
Open circuit cell voltage = specific gravity plus + 0.845

Fully Charged    1.275   
Fully Discharged1.150   
Charged Range    0.013   
Open circuit cell voltage     2.100

  1. %        1.275        2.120
  2. %        1.263        2.108
  3. %        1.250        2.095
  4. %        1.238        2.083
  5. %        1.225        2.070
  6. %        1.213        2.058
  7. %        1.200        2.045
  8. %        1.188        2.033
  9. %        1.175        2.020
  10. %        1.163        2.008
  11. %        1.150        1.995
Caution though, all this is just theoretical from research.

Have fun.

Curbie



Re: Battery SG question (3.00 / 0) (#6)
by zeusmorg on Thu Jul 02, 2009 at 05:21:41 PM MST

 Also not mentioned in these post yet, is the standard specific gravity chart is for 70-75 F. so if you're measuring at a different temperature adjustments are in order. The FAQ on lead acid batteries has a lot of useful information.


Re: Battery SG question (3.00 / 0) (#7)
by JW on Fri Jul 03, 2009 at 10:21:52 AM MST

I had a brand new battery of mine, tip over, in the back of my truck bed. I recently bought some new electrolite for it. On the side of the box it states the SG is 1.265 for the new electrolite. I only use a SG meter to monitor things when I add pure sulfuric acid(ACS) to the cells. I general only 5ml per 24 hours when I do this. I have noticed that you can raise the SG of a battery cell doing this. I use a small trickle charge when doing this after adding. Ive always supected other problems such as sulfation, when the SG is 1.275, and the batt has poor storage capacity. Dont think there much of a gain past 1.275 SG. Load tests are helpful, but also figure, if your batt has had more than 300 charge/discharge cycles its most likely shot.

[ Parent ]


Battery SG question | 7 comments (7 topical)
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