Bohemian Biker Blog

Application of Deltran Battery Tenders

by on Nov.19, 2009, under Battery Tenders

This post has been carefully assembled using information I’ve gleaned from Deltran Corporation’s website.  Specifically, information pertinent to the application of their Battery Tenders from the website Frequently Asked Questions (FAQ) page.  Bohemian Biker LLC is an Authorized Dealer for Deltran Corporation’s line of Battery Tenders and Accessories.  We are in direct communication with Deltran, and invite you to forward questions you may have in the form of comments to this post. 

Generally, the engine start batteries used in power sports range from 12 Ah to 20 Ah (Amp-hour).  To recharge a battery, it is necessary to replace the charge that the battery delivered the last time it was discharged.  The dimensions or units describing electrical charge are the Coulomb or, more conveniently…in the context of battery charging, the Amp-Hour (Ah).  A battery charger delivers charge (amp-hours) to the battery by using an electrical current (Amps) at its output over a period of time (Hours).  The numerical product of the electrical current and time period is the amount of charge delivered.  This is true in a general sense for any charger.

The Deltran Battery Tender Jr and Waterproof 800, as well as the Deltran Battery Tender Plus employ a 4-step charging program: Initialization, Bulk Charge, Absorption Mode, and Float Mode…which means they operate using 3 charge modes: bulk charge, absorption charge, and float charge.

In a manner similar to that of the Battery Tender Plus, the Battery Tender Jr. employs a higher level of sophistication in its use of electronic control to maintain a battery in a full state of charge over extended periods of time. Although its power output is somewhat less than the Battery Tender Plus, the Battery Tender Jr. employs a similar charge control method to keep the battery at full charge…while minimizing the long-term risk of overcharge and premature capacity loss. Typical trickle chargers are simply not capable of regulating the output voltage applied to a battery as the battery ages.  The Deltran Battery Tender Jr. is capable of charge maintenance on all lead acid battery types, including both AGM and GEL cells.

The Deltran Battery Tender Plus delivers a regulated, nearly constant 1.25-ampere output charge current during the bulk charge phase…and it has been specifically designed to accommodate the charging requirements of Absorbed Glass Matte (AGM) style batteries.  To achieve this the Battery Tender Plus switches from absorption charge mode to float charge mode when the charge current drops to 0.1 amps.  The result is that for an extended period of time, not to exceed 8 hours, the Battery Tender Plus output voltage will be held at a constant voltage that is significantly higher than the float voltage.  The maximum voltage output of the Battery Tender Plus is 14.4 to 14.5 volts.  Typical automotive electronic systems run between 14 and 15 volts with the alternator running.

Because of the slightly higher voltage recharge requirements of AGM batteries, and because AGM batteries require a longer period of constant voltage absorption, the Battery Tender Plus controls the output voltage at 14.4 volts…while it waits for either the charge current to decrease to 0.1 amp…or for the absorption charge mode control timer to expire.   The Battery Tender Plus battery charger holds the battery voltage at 14.4 volts until the charger current drops to below 0.1 amp, or until 8 hours has elapsed during the absorption charge period. Then the Battery Tender Plus goes back into float mode…where its output voltage is constant at only 13.2 volts.

For a valid calculation of charge returned, the electrical current at the output of the battery charger must be constant during the period of the calculation. This…and the amplitude of the charge current…are the critical features of a battery charger that determine how fast it will recharge a battery.

Once gain, the Deltran Battery Tender Jr and Waterproof 800, as well as the Deltran Battery Tender Plus are designed to recharge and maintain batteries commonly used in motorcycles and power sports equipment – typically 16 to 20 amp-hour batteries. The cold crank rating of these size batteries is typically 250 to 350 CCA (Cold Cranking Amps).  Used on a much larger battery…for example, a car battery rated at 650 to 900 CCA…with a capacity rating of 40 to 70 amp-hours…the time to fully recharge may be very long. Particularly on AGM batteries…the last 5% of recharge is the most difficult to deliver to the battery.  That is why it is important to extend the absorption charge period. Even with the 6 hour safety timer used on the Battery Tender Plus, a larger battery may have the higher, constant absorption voltage removed while the battery is still drawing much more than 0.1 amp. Once the Battery Tender switches over to the lower float voltage of 13.2 VDC, the voltage potential available to force the charge current into the battery is very low.  By this time, the rest state battery voltage is probably at 12.7 to 12.8 VDC. That leaves only 0.5 to 0.6 VDC to push the current. Near the end of the absorption mode, with the rest state battery voltage at the same levels, the charger voltage is at 14.4 VDC, leaving a voltage potential of 1.7 to 1.8 VDC to push the current into the battery. That’s almost 4 times the push available, compared to what’s available in the float mode. That’s why it takes so much longer to recharge a battery, once the charger switches over to float.

An automatic, well-regulated, temperature-compensated charger can keep a battery fully charged and at the same time minimize the risks of long-term damage to the battery due to either under-charging or over-charging.  The alternative is to let the battery internal losses run their course, which for most batteries means that they are fully discharged within a few months.  If you forget to recharge them periodically, and they become severely over-discharged, even due to only internal losses, the plates will become severely sulfated.  For many batteries, that means that they are permanently damaged.

Deltran’s recommendation is to use the Deltran Battery Tender Plus in Continuous Float Mode Charging applications: The line regulation characteristics of the Battery Tender Plus are excellent; less than 1% for line voltage between 115 VAC and 125 VAC.  This unit is temperature compensated and it has a special charging algorithm optimized for sealed, gas-recombinant, AGM, lead acid batteries. Numerous motorcycle owners have reported to Deltran over the years that their batteries have lasted 3 years or more.

I’ll be revising and adding to this post, as I glean more info from Deltran Corporation’s website!  Look forward to your comments!

We welcome email at:

These products are available through our new e-commerce website at:  

This is a link directly to the page listing the Deltran Battery Tenders above:

Solar Capitalist LLC is our sister company specializing in Deltran Battery Tenders (including solar powered models), as well as, Global SUNLINQ Portable Solar Chargers, and related connectors, leads, and cords – Capitalize on the Sun’s Energy !


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