[Napa Skip]

Why Good Batteries Go Bad, or "The Care and Feeding of Your Model A Lead-Acid Battery"

The care and feeding of lead-acid batteries is not very difficult but several things – other than quality of manufacturing - can shorten their life, namely plate sulfation, under charging, over charging, high discharge rates, electrolyte stratification, extreme temperatures, and low electrolyte levels.

The typical lead-acid battery consists of alternating positive and negative plates, separated by thin non-conductive (but permeable and porous) separators. Typically (for automotive lead-acid batteries) the positive plates consist of a lead-dioxide (PbO2 for those of a chemical bent) paste impressed into a lead grid while the negative plates are formed from a porous (high surface area) lead (Pb) paste, also impressed into a lead grid. The separators keep the alternating +ive and –ive plates from shorting against each other (e.g., during periods of high discharge rates when internal resistance causes heating of the battery and bowing of the plates; or from the growth of deposits – “dendrites” - on the surface of the plates during repetitive battery cycles).

Without going too deeply into the specific chemical reaction, during discharge the lead in the –ive plates combines with the electrolyte (sulfuric acid) to form lead-sulfate and hydrogen and release electrons, while the +ive plate lead-dioxide combines with the sulfuric acid, hydrogen and electrons to form lead-sulfate and water.

Put another way, as the battery discharges, the plates turn to lead-sulfate, the electrolyte turns to water and the flow of electrons from the negative plates to the positive plates makes your starter go roundy-roundy (that’s a technical engineering term). [This presumes electron-flow theory of electricity; if you subscribe to the “hole-flow” theory of electricity then the holes are created at the +ive plate and flow to the –ive plate; and no, your starter won’t rotate in the other direction. Good grief!]

Charging the battery reverses the process, resulting – in the perfect world – in lots of lead and lead-dioxide, no lead sulfate, and fully refreshed sulfuric acid electrolyte. However, as in every process, nothing is perfect (the lead-acid battery equivalent of 'entropy') so over time the plates tend to become increasingly sulfated (i.e., the charging process fails to completely reverse the lead- or lead-dioxide to lead-sulfate process). Additionally, mechanical vibration (as you bounce down our increasingly pot-holed roads with your marginally performing – or non-existent – shock absorbers) and repeated flexing of the plates (from thermal cycles induced by alternate deep discharges and subsequent recharging as you try to troubleshoot your non-starting engine before realizing you forgot to turn on the ignition key) cause the lead- or lead-dioxide paste to flake off the plates and settle to the bottom of the battery case, where – eventually – they will short out the bottom of the cell plates.

Therefore, the following is the generally recommended care of automotive lead acid batteries, realizing that – as with everything – you pretty much get what you pay for, so the manufacturing quality (not always reflected in the price) of the battery will often be the determining factor in battery life:

1. Keep them clean by wiping up any dirt, debris or spilled acid, and keep the battery terminals (and battery terminal to battery post connection) clean. In this regard the outside of the terminals can be coated with one of the commercially available battery post sprays or petroleum jelly; use of regular grease is frowned upon although I suspect there are any number of automotive batteries running around with chassis grease smeared all over the terminals);
2. Keep them charged (prolonged periods of discharge will tend to permanently fix the lead sulfate in the plates);
3. Keep the electrolyte level above the plate tops (by adding distilled water, inasmuch as tap water, with its high mineral and chlorine content, will – over time – tend to degrade the performance of the plates);
4. Avoid extreme discharge rates, which tends to overheat the battery and cause physical damage to the plates;
5. Avoid overcharging, which tends to (there is some disassociation of water into hydrogen and oxygen during charging) reduce the electrolyte level, concentrate the remaining electrolyte (i.e., increase the concentration of sulfuric acid, which leads to increased plate corrosion) and either expose the plates to air or otherwise damage the battery;
6. Avoid extreme mechanical shock, although conversely, moderate mechanical agitation does help mix up the electrolyte, which avoids electrolyte stratification which can result from long periods of non-use of the battery and – again – result in damage to the plates.

For long periods of inactivity, you might consider disconnecting the battery and/or hooking up a trickle (low amperage) charger. On my tractor (my Model A gets too much use) I use a simple timer to give a small (15 minute) freshening charge once a day except when I’m using the tractor every day. In the event you remove the battery from your A, place it on a piece of cardboard or wood rather than allow it to sit on the concrete floor.

Speaking of disconnecting your battery (we were speaking of this weren’t we?) the recommended procedure is to disconnect the ground first and connect the ground last, based on if you accidently short out the non-grounded terminal while removing/reinstalling it, you won’t have a path to ground if you have already removed/not yet installed the ground cable.

And, I suppose, it would be negligent not to address the modern-era safety precautions of working around lead-acid batteries, namely – before lifting the battery access cover in the floorboard of your favorite Model A – extinguishing all sources of open flame within 250 feet, donning OSHA-approved hearing protection, high-impact safety goggles, face shield, full-face respirator, acid-proof rubberized apron, acid-proof gloves and attaching a grounding strap to one of your more accessible bodily appendages (ouch!).

[Disclaimer: the above information derives from having served in submarines during a significant portion of the 1960’s, 1970’s and 1980’s, where the average lead-acid battery cell – if placed alongside a Model A – would extend above the roofline and where two such cells weigh about what a coupe weighs. With no disrespect to my Italian great-grandfather and great-grandmother, that’s what – to paraphrase an Alka-Seltzer commercial – would be described as “Mama Mia - that’s a one a biga battery cell.” And even nuclear submarines need batteries, else whilest out in the big pond and you suffer a loss of reactor power (generally the result of a training drill, but occasionally the real thing) you don’t have electrical power to restart the reactor. Also, submarine batteries give off-watch electricians something to do – namely hopping cells - measuring battery cell specific gravities while crawling along for a couple of hours crouched over in the battery tank – while everyone else who isn’t on watch or in the rack, is in crew’s mess watching a flick and eating ice cream and sticky buns. And, lastly, it wasn’t my intention to recommend disregarding reasonable safety precautions while tending to one’s automotive – or submarine, if you have one – battery, but sometimes it makes you wonder how any of us managed to make it this far in life intact.]

Zzzaaap!

[Sorry for the long post; slow day out here on the left coast and I'm waiting for my Model A battery to be recharged...]