This post on how to parallel charge a dead motorcycle battery is a continuation of our segment on Motorcycle Battery Testing but can be applied to all types of lead acid batteries. It is a temporary yet important aspect to diagnosing a bad battery. It also helps answer the question: Can I test my motorcycle battery with just a charger & voltmeter? The short answer is YES, kind of...

If you have a more permanent parallel setup, such as what is used by boat or RV owners, you should jump over and read our Perfectly Balanced Charging tutorial. You will discover how a simple tweak to your set up could save you untold lost dollars and time.

But back to diagnosing a bad battery... It is absolutely amazing how many consumers and so called professionals misdiagnose a battery as "bad". A large percentage of those so called failures were batteries that were unnaturally discharged and salvageable or were tested by an inexperienced or shady professional.

Dead Battery Parallel Charge MethodSo What is this Parallel Charge?

A parallel battery charge is when you join two batteries of the same nominal voltage (i.e. two 12V batteries) connected positive to positive and negative to negative with a smart charger. In the case of a possible warranted battery, we are trying to revive the depleted, 'dead' or suspect battery.

You would use this technique when the battery voltage is too low for your charger to properly detect there is a 12 volt battery present. On a 12V battery, this can range from 1V to 10V depending on the brand and age of the charger. Surprisingly many of the so called smart chargers have a fairly high detection threshold. And several that indicate they have a lower threshold don’t seem to meet their own standard. The best low voltage detection charger we have encountered is Schauer’s Charge Master Series which includes the CM1A, CM6A and CM12A.

In fact we actually discovered the Charge Master capability in low voltage detection quite by accident. Our 27 ft. box truck requires 3 group 27 size batteries. One had developed a short and drained all three of the batteries while the truck sat waiting to go on its next run. All three of the batteries were severely discharged ranging in voltage from 2V to 4V and we only had one larger capacity charger. We were using a Noco G26000 and had to place the depleted batteries in parallel to get the charger to recognize there was a 12V battery present. We had some blemished motorcycle batteries that still had good voltage but could not be sold as new so we used those to establish the parallel connection.

Since we needed to get the truck running quickly we went and got a CM16A off our shelf (which has been replaced by the CM12A now) and attached it to the battery. We did not have another set of cables to create a parallel charge so we hoped for the best. Our hopes were dashed as the charger appeared to be doing nothing. The power light was on and that was it. No fan sound. No movement on the LED lights indicating bulk charge was initiated. There was nothing telling us it had begun to charge. Since it was the end of the day we left everything as it was and went home.

The next morning we were stunned to find the battery, attached to the CM16A, showing fully charged. The LED lights indicated it had completed the charge and was floating the battery. The voltage on the battery confirmed what the charger was saying. The battery load tested normal. We were shocked and amazed and called Schauer to tell them what transpired. They chuckled and graciously told us they were glad to hear it worked out. Really, what I think they wanted to say, was more along the lines of “yeah, we know!”

The take-away of this is twofold. Charger manufacturers have different ranges of low voltage detection. This is meant to prevent someone from accidentally (or deliberately) using a 12V charger to charge up a 2V, 4V, 6V or 8V battery. Second, the parallel battery charging technique can be used with any type or style of lead acid based battery. It does not matter if they are deep cycle RV batteries, motorcycle, automotive starting batteries, gel, AGM, conventional or solar batteries. Parallel charging works! If your 12v battery is lower than 10V it is worth a try before you take the time to pursue the warranty.

Is there a right and wrong way to set up the parallel charge?

We used to tell our customers it did not matter. But several years ago we discovered (by an astute observation or you could say by accident again) that how and where the charger was connected made a difference in whether the depleted battery would accept the charge.

In this discovery we were using one of our favorite chargers, the XC100-P by PulseTech. We were working with an Adventure Power motorcycle battery (which is now merged with Kinetik). I do not recall the precise voltages but do remember the starting voltage was around 4V or 5V. The parallel system was set up that morning and left to do its thing throughout the day. Towards the end of the work day it was disconnected and the battery voltage checked. There was minimal change.

The next day someone noticed an older looking battery on the shop bench and surmised someone got distracted and it needed to be parallel charged. At the end of the day it was again disconnected and the battery showed full voltage! The ensuing discussion and after several more careful observations utilizing multiple charger brands we determined that how the charger is connected makes all the difference in the world.

So without further ado the following are the four steps to proper parallel charging when you encounter a 12V battery registering less than 10V (the depleted battery). You will need a smart (maintenance) charger and a voltmeter would be beneficial:

Parallel Charging a 'Dead' Battery
Step #1 Locate any 12V nominal battery registering 12.4V or higher. If you don't have a multi-meter simply use a 12V battery you know to be working in its application. We will call this the ‘assisting battery’. The battery does not need to be disconnected from its application, but sometimes it is wise to do so.
Step #2 Connect a set of jumper cables positive to positive and negative to negative to the depleted and assisting battery. [If you left the batteries connected to a vehicle DO NOT turn on any engine. To avoid any possibility of system interference it is best to isolate both batteries if possible].
Step #3 Connect your appropriately sized smart charger to the terminals of the good assisting battery.
Step #4 Leave the batteries connected until the charger says the charge is complete or for up to 12 hours on severely depleted batteries. One to three hours is NOT enough time!

This may be a good spot to remind you about our tutorial on Perfectly Balanced Charging of 2 or more batteries paralleled together (there is a link in the second paragraph of this article). That tutorial is more detailed and includes imagery of a sample four battery configuration. Many in the solar, boating and RV community could benefit from this tutorial and perhaps extend the useful life of their RV & Marine Batteries by making necessary adjustments to their system.

Bonus story: Teaching an Old Dog a New Trick

From time to time a customer will call us back or email to thank us for “teaching an old dog a new trick.” It's always a nice feeling knowing you have done your job well enough to teach others some of the tricks learned from our hands on experience. In many of these cases the individual left our initial phone conversation very much skeptical but still willing to “jump through the hoops” to get a battery warranted. The lack of trust and growing disdain for the process is often so thick you could cut it with a knife.

A day or so later when they call back, the tone in their voice is entirely different. They are excited yet perplexed. They are fascinated and curious to know more of the secrets in the battery universe. Elated and very much satisfied may be the best way to describe what we hear.

Obviously there is more to testing a motorcycle battery than simply connecting two batteries together. But if you can get it running by applying this simple trick most of you will by happy and be on your merry way. There is no need for further testing in your mind. Some of you will have further questions such as "Can I trust this battery?" Absolutely you can trust this battery! For that battery to have been at such a low voltage it would have had to respond to some sort of external stimuli. A battery in and of itself will not discharge to those low levels. When there is no physical damage to the battery cells, it can be revived with no ill effects.

This was just a zoomed in view of one possible phase of testing you could and should expect. Ideally you should complete this step prior to calling in for a warranty. Hopefully it was presented in a way in which you feel you have added another tool to the toolbox. The final segment in this battery testing montage covers what you can expect trying to complete a warranty from the other side of the country.