The Ultimate Battery Charger

Electrical and electronic topics for small boats
Posts: 9008
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

The Ultimate Battery Charger

Postby jimh » Mon Feb 06, 2017 10:10 am

The P12 Battery Charger from Blue Sea Systems may be the ultimate 120-Volt AC-operated 12-Volt-DC marine battery charger. The P12 can individually re-charge three 12-Volt batteries of similar type, providing a maximum total output current of 25-Amperes or 40-Amperes depending on model. The P12 Battery Charger has several unusual features.

The battery charging method is described as a four-stage process. The four stages of charging are called:

--bulk, when the full-output of the charger is pushing as much current as it can into the battery, until the battery reaches a state of charge of about 75 to 80-percent;

--absorption, when the charger begins to taper off its charging current, as charging continues to 100-percent;

--pre-float, a new stage unique to this charger, in which an intermediate voltage, higher than the float voltage but lower than the absorption voltage, is applied to one or two of the attached batteries while the third battery remains in the absorption stage; and,

--float, when a carefully regulated voltage is maintained to keep all three fully-charged battery at maximum charge.

The voltages during these stages are also compensated for temperature. If the battery temperature is cold the voltages for charging are increased somewhat, and if the battery is a warm the voltages are decreased. Temperature compensation of this type is typically recommended by battery manufacturers to get the best possible charging of their batteries.

In addition, the P12 charger contains four pre-set profiles for charging voltages in the four-stage process, with provisions for batteries of various constructions:

--flooded lead-acid
--gelled electrolyte lead-acid
--absorbed glass mat or starved electrolyte lead-acid, and
--thin-plate pure-lead lead-acid (see more on this below in follow up article)

If none of the pre-set profiles are suitable, the user can create his own custom charging profile to match the recommended voltages for charging a battery as provided by the battery manufacturer.

The P12 can also interface with Blue Sea Systems automatic charging relay (ACR) devices to insure that all batteries are isolated during charging. It does this by preventing any of the ACR devices from paralleling a battery with another during charging using the feature called Start Isolation in the ACR devices.

The P12 Battery Charger has a large display screen to provide status information, offer diagnostic messages, and to permit user programming of the charger operation, such as the individual charging profiles for each battery. If access to the main display is not convenient, there is an optional accessory, the P12 Battery Charger Remote, that allows for a second and somewhat simplified status display and some limited control functions to be provided at a location remote from the actual charger. A 25-foot interconnection cable is provided; cables as long as 150-feet can be used.

All these features come at a price: the P12 Battery Charger has an MSRP of $550 for the 25-Ampere model and $700 for the 40-Ampere model. It is also a rather massive device, with a housing of about 13 x 9 x 4-inches and weighing 13-lbs. The model 7520 remote display and control has an MSRP of $120.

If your boat spends lots of time at a dock and connected to shore power, the P12 Battery Charger is probably one of the best solutions for providing proper battery charging and care.

Blue Sea Systems P12 Battery Charger
p12.png (128.06 KiB) Viewed 9259 times

More information can be found at the Blue Sea Systems website. Visit

Posts: 9008
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: Thin-plate Pure-lead AGM Battery Construction

Postby jimh » Mon Feb 06, 2017 11:15 am

The term "thin-plate pure-lead" (TPPL) appears to refer to a special form of absorbed glass mat (AGM) lead-acid battery in which the thickness of the lead plates is reduced compared to normal construction. The thinning of the plate material allows for a higher number of plates to be used in standard case sizes, thus increasing the power storage density of the battery. It is claimed that by use of high purity lead the manufacturing of thinner plates is made possible. The use of lead with extremely high purity is also recognized as a means of reducing the self-discharge rate of a lead-acid battery.

Examples of a thin-plate pure-lead (TPPL) AGM lead-acid battery are the ODYSSEY EXTREME SERIES 12-Volt AGM battery and the NORTHSTAR NSB-AGM 12-Volt AGM battery.

Posts: 9008
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: The Ultimate Battery Charger

Postby jimh » Wed Feb 08, 2017 2:19 pm

For smaller boats, another Blue Sea Systems battery charger may be more applicable: the BatteryLink Charger. The BatteryLink Charger product is a designed for a two-battery system. It provides a dual charger output and an automatic combiner relay. The maximum output current is 10-Amperes. The charging profile is three-stage; there is no pre-float stage. Blue Sea Systems says the charging profile is suitable for use with flooded-cell, AGM, and TPPL batteries. There is no clear mechanism to select a particular type of battery and its charging profile. No custom custom profiles for specific batteries can be created. Temperature compensation is provided by one remote temperature sensor. The combiner relay is rated for 65-Amperes.

The BatteryLink Charger device should be a good solution for typical outboard boats with two batteries. The MSRP is $200. For more information and comments on the BatteryLink Charger device, see my earlier article at

Posts: 607
Joined: Tue Oct 27, 2015 9:57 pm
Location: LSD Lower Slower Delaware

Re: The Ultimate Battery Charger

Postby porthole » Fri Feb 10, 2017 10:26 pm

During your research did you see what the the output voltage was and if it was adjustable?
2016 World Cat 230DC
1999 Outrage 21, Yamaha SW Series II 200
1997 Outrage 18, Yamaha 125
1983 15 SS, Honda 50

Posts: 9008
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: The Ultimate Battery Charger

Postby jimh » Sat Feb 11, 2017 9:08 am

In the four stages of the Blue Sea Systems P12 Battery Charger, the output is only voltage regulated in three of the stages:

--BULK: apparently no voltage regulation used here as the charger is trying to push as much current into the battery as the battery can accept and as the charger can supply; this is called a constant-current stage; this stage continues until the battery terminal voltage rises to the absorption state voltage;

--ABSORPTION: the charger output is regulated to the proper voltage as determined by profile selection, and charging continues but at a lower current; the charger remains in this stage until several parameters are satisfied, including a time duration parameter and the amount of current flowing; these parameters are called ABSORB TIME and END ABSORB AMPS. The time can be varied from one to five hours. The END ABSORB AMPS is typically set to be about one-percent of the battery's Ampere-hour capacity. For example, if you have a 70-Ampere-hour battery, the current to trigger end of ABSORPTION mode would be 0.7-Ampere. If there are any static loads on the battery, the END ABSORB AMPS should be modified to account for that additional current flow in the circuit. The instructions recommend setting the time and current parameters based on actual measurements of the particular batteries in use as they are being charged by the P12 charger.

--PRE-FLOAT: the charger output is regulated about 0.5-Volt lower than the absorption state;

--FLOAT: the charger output is regulated to the manufacturer's recommended float voltage for the battery type;

There are four profiles preset and a fifth profile may be customer defined. Here are the voltage settings:

PROFILE                    VOLTAGE
Flooded Lead Acid 14.5 13.5
Absorbed Glass Mat 14.35 13.3
Gelled Electrolyte 14.1 13.5
Thin Plate Pure Lead 14.7 13.6
User Adjustable 12.5 12.5 (Default settings)

The User-Adjustable profile can be set to user-defined voltage points for absorption and float. The TPPL voltages are taken from the Odyssey and Northstar battery literature. The voltages are based on temperature being 77-degrees-F.

Also note that the selection of a profile setting adjusts ALL outputs to that setting, so the charger should not be used to charge a mix of different battery types; all three batteries being charged should be the same type. The instructions contain several warnings advising not to mix battery types.

The design of this charger and the many parameters in the charging process that can be adjusted are worthy of the description I have used: the ultimate battery charger.

The concept of a battery charger having different modes of charging and changing among those modes as the battery responds to the charging current is nothing unusual or particularly excessively complicated in modern battery management. Particularly useful in the P12 chargers is the provision for several presets and the ability to adjust those parameters to suit a particular battery's behavior. With modern batteries costing as much as $400 each, it seems prudent to use battery management methods that extend their useful service life and provide the best energy storage. To use a $550 charger to maintain a three-battery bank of $400 batteries is not excessive; it is the same investment as using a $45 charger to maintain a $100 battery. (For example, the Firefly Lead-Acid Carbon Foam Group 31 battery is $486. Would you charge this with a $40 Walmart charger?) By using better charging techniques, a P12 charger would easily extend the service life of the batteries significantly, and pay for itself in saved battery replacement costs. Using a "simple" charger which does not provide good battery management could easily significantly reduce the useful service life of a battery and lead to higher overall battery costs.

Posts: 80
Joined: Sun Mar 06, 2016 1:18 pm

Re: The Ultimate Battery Charger

Postby OldKenT » Mon Aug 06, 2018 6:19 am

If the charger Jim has described doesn't work for you, take a look at MinnKota Precision chargers:

https://minnkotamotors.johnsonoutdoors. ... s?id=13971

I have used a 2-bank model for a few years and find it to be very reliable. It does not have a display screen, but it does allow the user to select a different battery type for each bank. It is not as flexible as the one Jim has described, but it is available in one to four bank models with differing charging rates available for each model so you should be able to find one that works for you.