Skip to the main content.

Genset Starting Education Module #4

Genset Start Battery Strengths,  Weaknesses & Use Strategies 

William F Kaewert | SENS – Stored Energy Systems LLC 

Lead-acid battery strengths, weaknesses and strategy of use 

Two different types of batteries, lead-acid and Ni-Cd, are commonly used to start gensets. These two  technologies have different characteristics that specifiers and users need to understand in order to  successfully use each type.

The lead-acid battery is readily available, low in cost and likely to fail suddenly at end-of-life. The most  successful approach to using lead-acid starting batteries is to regard them as consumables needing  regular replacement. Regardless of replacement frequency, correct charging and battery maintenance  remain essential because new batteries can fail as frequently as a few months after installation if not  properly charged and maintained. 

Summary of strengths and weaknesses of lead-acid start batteries 

Strengths Weaknesses
Low initial cost 
Can fail suddenly
Good energy density 
Plates degrade 
• Positive plate corrosion 
• Negative plate sulfation
Standardized, small size footprints
Susceptible to extreme temperatures
Standard container sizes 
Limited life of 3-5 years under ideal conditions
Widely available at short notice 
Shelf life1 of 3-6 months maximum
Integrated as OEM equipment 
Lower system reliability than Ni-Cd
Relatively easy to charge to full capacity
Easily recycled

Ni-Cd battery strengths, weaknesses and strategy of use 

Ni-Cd technology is inherently more robust than lead-acid technology, does not fail suddenly like lead acid and is very long-lived. The higher up-front cost and long life expectation of Ni-Cd batteries mean that  they would never be considered consumables. Unlike lead-acid batteries, though, Ni-Cd cells are not kept  in stock at local battery distributors, so in the event of a cell failure, replacement could be days or weeks  away. When a cell fails, users must choose to either jump out the bad cell or deploy a temporary lead acid battery until the replacement cell arrives.  Ni-Cd batteries require a well-defined commissioning charge to achieve the manufacturer’s specified  performance when installed. These parameters are typically provided in the battery maker’s installation  and operation instruction manual. 
Defined as time sitting idle in a warehouse after last charge. Shelf life is shortened by high ambient temperature. 

Some variants of Ni-Cd2 are much more difficult to fully charge than lead-acid types because recharge  efficiency is worse than in lead-acid batteries.3 The user manuals for some Ni-Cd types specify that two rate charging4 is mandatory to achieving manufacturer’s specified performance. Battery chargers used  with Ni-Cd batteries therefore should be specified to include automatic boost charging after discharge.  

As with lead-acid batteries, correct charging and battery maintenance are essential.

Summary of strengths and weaknesses of Ni-Cd start batteries 

Strenghs Weaknesses
No sudden failure mode 
High cost
Survives extreme temperatures 
Much larger footprint than lead-acid
Resistant to mechanical and electrical abuse
Poor availability (none are made in the US),  meaning a long wait to replace failed cells
Gradual end of life 
Pocket plate type Ni-Cd is more difficult to charge  than lead-acid types
Resistant to overcharge & undercharge abuse 
Requires proper commissioning charge to perform  properly
Longer (than lead-acid) shelf life 
67% more cells needed for same voltage as lead acid

Summary of key points

1. Lead-acid battery: 
• Strengths include that it is readily available, is made in standard sizes, and is low cost. • Weaknesses include sudden failure at end of life, loss of life when hot, loss of  performance when cold, and short shelf life. 
• The most successful strategy to achieving reliable engine starting with lead-acid starting  batteries is to regularly replace them well ahead of the date of expected failure. 
2. Nickel-cadmium battery: 
• Strengths include inherently robust design and construction, no sudden failure  mechanism, long service life and relatively long shelf life. 
• Weaknesses include higher initial cost and larger footprint than lead-acid, and lower  availability of replacements. 
• The most successful strategy to achieving reliable operation with nickel-cadmium is  committing to use Ni-Cd batteries in the first place, then continuing to maintain them.  
Pocket plate Ni-Cd technology is more difficult to charge than newer Sintered PBE or fiber plate Ni-Cd technology. Recharge efficiency of pocket plate Ni-Cd batteries is around 70%, meaning that the charger must deliver at least  140% of the ampere-hours (AH) withdrawn from the battery before the battery is fully recharged. The recharge  efficiency of very shallowly discharged batteries is even lower because replacing the last AH of capacity is always  more difficult than replacing the first AH when the battery is discharged. See SENS Genset Starting Education  Module #6: Battery Charging Basics for additional information. 

Two-rate charging is the most effective way to reduce charging time. Ideally, two-rate charging temporarily  increases charging voltage above the normal float voltage setting during initial battery recharge. This is called “boost charging”. Excess voltage applied to the battery compensates for voltage lost to the battery’s internal  resistance. Operating at the higher boost voltage allows the battery to accept the charger’s maximum current longer than it would at float voltage. A correctly engineered charger automatically reduces the charger’s voltage to  the correct float voltage value when the battery reaches full charge. See SENS Genset Starting Education Module  #6: Battery Charging Basics for additional information.