After removing my Z's car cover I put a voltmeter on the battery terminals to see what the voltage was. For some unknown reason, I always thought that a 12 volt battery would probably have a stored voltage somewhere around 12.4v - 12.7volt. SurpriZe. I was wrong! The meter reading was 13.47 volts. So I wondered, was the "float charger" that was maintaining my battery over its winter hibernation putting out too much voltage/current? After some research on what the proper charger outputs should be, I found out that a maintenance charger should be putting out 13.2 -13.5 volts for a lead/acid 12v. battery. Other types of batteries require different voltage outputs to properly maintain them at their full potential. I checked the three float chargers that I have and came up with three different outputs. 12.2 volts, 12.7 volts and 13.7 volts.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

I was always surprised to see this too. The advertised "12 volts" is the operational minimum which the battery must remain prepared to deliver, but they often store a few volts more than that until called upon.
A measured 12+ volts is the indication of a healthy battery, but they all vary in cold cranking amps, amp hours and other obscure measurements.

And always remember, "Do as you aughter, add acid to water" to prevent a severe hypothermic reaction ("explosion"). If you have to add water to the acid, do it very slowly and in minute measures. Some guys extract some H2So4 from their battery and mix it with some water which is already waiting in a container, then carefully replace that mix back into their battery.

You can actually drop an open lead/acid battery into a pond and nothing will happen. But if you add water too quickly to the battery acid cell, you can wind up wearing it all over your face and hands.

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1970 240Z

Distilled water too for batteries, correct Frank?

I'll also add that I've found over the years that if I measure less than 13V in my car battery, even if I'm experiencing NO issues at that time, in the near future some issue will arise with the battery or charging system. It's an early indicator for me, usually means it's a good time to double check to make sure you have jumper cables on board still.

Howie, 13.5 volts is exactly where your battery voltage should be. It's not indicative of an overcharging battery tender, but rather a properly functioning one.

Jay

Jay. I wasn't aware that a 12 volt battery at rest should be reading 13.5 ish volts. I'm guessing it's time to retire the two float chargerZ whose output is less than 13 volts. Thanks for your input.

Howie

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

It's nearly summer again Howie, don't forget to reverse your battery so the air conditioner works instead of the heater.

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1970 240Z

You're welcome Howie, take it with a grain of salt. Just sharing my experience, I don't consider myself an expert on batteries but I've had my share of vehicles over the years and dead batteries to go along with them.

In high school and college I worked in an auto parts store part time and I remember testing the batteries on the rack in the store. 13.48 volts was what I measured in every one of them.

I would be curious to see if one of your chargers that puts out less than 13v can charge a battery to 13.5? It might, I don't know. I believe it's the amperage (current) that actually flows and recharges the battery, the voltage is the potential.

An electrical engineer I knew explained electricity to me like this (again, I'm no expert). He said picture electricity like water in a pipe. The voltage (potential) is like the water PRESSURE in the system, the amperage (current) would be the VOLUME of water that flows through.

Jay

Also Frank, that's funny about reversing the terminals for ac or heat haha.

Reversing the leads does make DC electric motors run backwards though. Power window motors are controlled that way to make the glass go up or down.

Jay

You're right again Jay, unless the car is an early Cadillac, Lincoln, or a French Citroen, in which case the windows are hydraulic.

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1970 240Z

Frank. Got it Buddy. Thanks for the reminder.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

I just looked that up Frank, another new one on me.

Jay. I'm going to connect the 12.5v charger to the 13.5v battery for a few days to see if the reading I get will stay at voltage or if the charger actually pulls it down to 12.5v. It should be an interesting experiment without any detrimental effect on my battery. Worst case scenario, I have to charge the battery back up to 13.5v.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Good idea Howie, I'm interested to see the results.

Jay

Update:
I placed my 12.7v float charger on my new 13.48v battery for 7 days to see if it would maintain its present charge. The voltage dropped about 0.1v per day, so that after seven days the voltmeter was reading 12.78v. That's still an acceptable number to start the engine, but...

So... I am going to assume that a float chargers output voltage should be checked to make sure that it's reading between 13v - 14volts before connecting it to your battery. My 13.7 volt float charger is now back in service again.

Eagerly waiting for warmer dayZ.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Thanks for updating this Howie, I was wondering about it.

That's interesting. So the float charger actually reduced the voltage of a fully charged battery? How about that. I'm going to have to remember that for the future.

Jay

Electrical current is just like water; it takes the easiest path to the lowest point (least resistance). A simple transistor can prevent high charges from draining into lower charges, and most battery chargers have those or a one-way diode.

The old Regulators offered an electrical-mechanical disconnector to prevent the battery from discharging back thru the generator when the engine was off. Today we use transistors or diodes and Y-phase alternators to accomplish the same prevention.

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1970 240Z