removing surface charge

http://www.jgdarden.com/batteryfaq/carfaq.htm I'm bumping this for this worthwhile reference (IMO), and 'cos it's a good place to put it.... Ironically, I now think I know where calitech got the OP "turning on the high beams for five minutes, then waiting like 15 minutes" info for removing surface charge. But do AGM/VRLA batteries have surface charge...? (See below.) Regarding Surface Charge, I have extracted the relevant text below from 4.3. Remove Surface Charge which is part of carfaq4.htm = Car and deep cycle battery FAQ (as updated 2nd January 2010). This is Bill Darden's famous info that is often referenced as being at http://pweb.uunet.de/william.darden/carfaq.htm which is now http://www.jgdarden.com/batteryfaq/carfaq.htm (I have an older uunet copy (of Part-9) and went looking for Part-4 - finally finding the new & updated site.) I was glad to see so far that my advice has not been wrong. Like, last night I saw someone saying batteries should NEVER be paralleled when idle (ie, when not charging or supplying) because even when matched, they will differ and die prematurely. Mind you, if I read the lot, I'll probably find some of my bads! The following is extracted from Bill Dardner's carfaq4 "4.3. Remove Surface Charge" (with my added bolding): Surface charge (or "counter voltage") is the uneven mixture of sulfuric acid and water along the surface of the plates as a result of charging or discharging as the electrolyte has an opportunity to diffuse in the pores of the plates. It will make a weak battery appear good or a good battery appear bad. Larger wet lead-acid batteries (especially over 100 amp hours) could also have electrolyte stratification where the concentration of acid is greater at the bottom of the cell than near the surface. The Open Circuit Voltages (OCV) will read higher than they actually are. Stratification can be eliminated by an equalizing charge, stirring or gently shaking the battery to mix the electrolyte. So will an electrolyte-less AGM/VRLA have Surface charge (counter voltage)?    I'll have to read more.... (or does anyone else know?) And despite years of intent, I have yet to charge one of my 10 year old AGMs and find out! (They have been charged yearly, I just never tested for surface charge - though I can't recall the +1V often seen on wet batteries.) But I can imagine some surface charge - even if literally "surface" - ie, plate capacitance (even though this should self-discharge in seconds...) And herewith the rest of the info under 4.3.... A surface charge can be eliminated by one of the following methods after recharging a lead-acid battery:

- Allow the car or deep cycle battery to sit (or rest) without discharge or charge for between two and eight hours at room temperature, if possible, to allow for the surface charge to dissipate. (Recommended method.)

- For car batteries, turn the headlights on high beam for five minutes and wait ten minutes.

- For car batteries, apply a load with a battery load tester at one-half the battery's CCA rating for 15 seconds and then wait ten minutes.

- For car batteries, disable the ignition, turn the engine over for 15 seconds with the starter motor, and wait ten minutes.

- For deep cycle batteries, apply a load that is 33% of the amp-hour capacity for five minutes and wait at least ten minutes. Note that all state wait ten minutes (except the recommended 2-8 hour wait). I like the 15-second cranking (plus 10-minute wait) as this is fast and convenient (for vehicle mounted batteries). And I expect that the voltage reading immediately after cranking will be far more indicative than the typical +1V seen after charging, though the post-cranking will be pessimistic. (After removal of their load, batteries self-recover to some extent - ie, their voltage increases.) Anyhow, for any battery related information, I highly recommend Bill (JG) Darden's info.

And FYI update on my AGM Surface Charge.... after intense scientifically controlled testing.... Last night I charged my two ~10 year old Yuasa UXH38AH-12V AGM batteries from an 8A charger in the bathroom. They had been ignored for an indeterminate period starting last decade (probably at least 12 months ago) and had voltages of 12.34V & 12.66V respectively. After charging each for an unrecorded time, the charger was disconnected after reading ~14.8V for one, and noting 15.4V on the other whilst brushing teeth (mine; and in situ). (NB: The electric tooth brush used an independent power source.) In the first "disconnect charger" case, I thought of MY Golden Rule never to exceed 14.4V when charging AGMs. In the second "disconnect charger" case, I chose not to think of my nee-Golden Rule. However, in both cases it was observed that their OC (open circuit) voltages quickly approached ~13.7-13.8V (about 1V above "full charge" voltages). From there they slowly reached ~13.2V within a few minutes. I then connected a 0.44A fan and later a 3A water pump to hasten the "surface removal" process. (Ignore teeth enamel and brushing - that was in the previous block & over 4 paragraphs ago. That subject is closed - no further decay etc puns.) Although the loads increased the rate of decay, I got bored around 13.1V, disconnected the loads, and kissed the terminals goodnight. [ The official record states that at 13.1V, "extreme fatigue caused by rigorous scientific testing took its toll and the esteemed tester retired for the night (without recovering expenses)". ] Approximately 12 hours later and the OC batteries are 12.76V & 12.80V respectively. (Ambient temperatures: Currently 21C. Last evening 32C. Overnight 19C minimum.) My conclusion is that AGMs do exhibit surface charge similar to wet cells, however: - the AGM's initial surface charge decay is much faster (my estimated real 5AH "12V-40AH" car battery holds its surface charge MUCH longer!) - I strongly suspect that Bill Darden's explanation of Surface Charge being cause by an "uneven mixture of sulfuric acid and water along the surface of the plates" is not correct for AGMs, however the root cause may be the same. I further suspect that the AGM is more likely to exhibit capacitive behavior than wet lead acids due to less conductive medium between plates (ie, electrolytes). As to how AGM and wet lead acids compare against each other in accessing their (audio/stiffening) capacitor equivalence with respect to "charge" is inconclusive. Wet cells seem to have more initial surface charge due to uneven plate-electrolyte distribution. AGMs may have greater "plate capacitance" (ie, like a capacitor). AGMs may also have uneven plate-charge distribution after charging similar to wet cells. AGM surface charge (or equivalent/other) may increase closer to their idle (steady state OC) voltage - in particular - relative to wet cells. (IE - AGM voltage initially decayed faster, but then seemed to hold up well.) Certainly from observation of voltage decays above "full battery voltage" above (ie, above 13.0V) and from observations or wet cells elsewhere (ie, Le Co-Pit of my car), I suspect the combination of capacitive & surface-charge charge in an automotive battery to be the equivalent of a VERY VERY large capacitor. Suggested next test: power/charge capacity of a wet cell, AGM, and large capacitor (eg, 1F - 10F etc) above 13.0V or 12.8V from 14.4V or 15.4V be compared. The lower voltages should be above the system voltage/s where the battery determines the system voltage (ie, by chemical conversion). The upper voltage/s should be the system's charge or operating voltage - ie, 14.4V max for normal vehicles; 15V or higher for SPL competitions etc. Then: Testing of "battery lag" - ie, any hi-load voltage dip whilst the battery changes from capacitive & surface charge energy to chemical energy. And Then: If the above suggest real-performance inferiority of the battery, compare ESRs and its dynamic effect in real-life extremes. Note that battery and capacitor costs must be included (as well as their size, manufacturer, model, batch etc as done with all above testing). Then there are comparisons for batteries that are under full charge - say at 70-80% capacity for crankers, or 20% capacity for deep-cyclers. But lets crack those Chinese Take-Away games first.