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Anonymous
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THE COST OF BATTERY POWER...
The cost of portable battery power is very expensive when compared to mains power available from a wall receptacle. The typical daily energy consumption of a household is 25 kilowatt-hour (kWh) at a cost of US $0.05 to 0.10 per kWh. In contrast, the table below shows the cost per kWh using non-rechargeable cells.
AAA Cell AA Cell C Cell D Cell 9 Volt
Capacity
Drcell Alk 1.1Ah 2.5Ah 7.5Ah 14.3Ah .6Ah
Energy 1.4Wh 3Wh 9Wh 18Wh 4.2Wh
Cost/Cell
Retail(US$)$1.25 $1 $1.6 $1.6 $3.1
Cost/Kwh $890 $330 $180 $90 $730
The average 9 volt rechargeable battery has a capacity between 120 mah to 170mah (.15Ah ave). Given the normal life of alkalines on a Headhunter PI (8-12 hours) the nimh rechargeable battery will last 2 to 3 hours. For a 4 hour hunt, you will need at least 2 sets and will be very low on the charge towards the end. This may be inconvenient for some.
The average rechargeable AA battery battery now has 2100 mah or 84% of the capacity of a Duracell AA alkaline. Given the 20 to 25 hour battery life of alkalines on the average AA powered metal detector, you will probably be able to hunt at least twice for 8 hours before needing to recharge. Not to mention that nimh will allow you to top off the charge once you get home and continue hunting indefinitely before a full charge. The downside hear is that nimh have a self discharge rate. It is best to use your rechargeables at the most a week after charging to get something close to the rated capacity. This is acceptable to some and incovenient for others. Its your choice.
NOTES ON SELF DISCHARGE:
Alkaline batteries stored at "room temperature" self discharge at a rate of less than two percent per year. So normally refrigerating or freezing them will only help maintain their charge by a tiny amount. Hardly worth the effort of chilling them. However, if alkaline batteries are stored at higher temperatures they will start to lose capacity much quicker. At 85 degrees F they only lose about 5% per year, but at 100 degrees they lose 25% per year. So if you live in a very hot climate or are storing your batteries in a very hot location, it may be worthwhile for you to store your alkaline batteries in a refrigerator instead.
NiMH and NiCd batteries self discharge at a MUCH faster rate than alkaline batteries. In fact, at "room temperature" (about 70 degrees F) NiMH and NiCD batteries will self discharge a few percent PER DAY. Storing them at lower temperatures will slow their self discharge rate dramatically. NiMH batteries stored at freezing will retain over 90% of their charge for full month. Water damages nimh batteries, so do not freeze them.
The cost of portable battery power is very expensive when compared to mains power available from a wall receptacle. The typical daily energy consumption of a household is 25 kilowatt-hour (kWh) at a cost of US $0.05 to 0.10 per kWh. In contrast, the table below shows the cost per kWh using non-rechargeable cells.
AAA Cell AA Cell C Cell D Cell 9 Volt
Capacity
Drcell Alk 1.1Ah 2.5Ah 7.5Ah 14.3Ah .6Ah
Energy 1.4Wh 3Wh 9Wh 18Wh 4.2Wh
Cost/Cell
Retail(US$)$1.25 $1 $1.6 $1.6 $3.1
Cost/Kwh $890 $330 $180 $90 $730
The average 9 volt rechargeable battery has a capacity between 120 mah to 170mah (.15Ah ave). Given the normal life of alkalines on a Headhunter PI (8-12 hours) the nimh rechargeable battery will last 2 to 3 hours. For a 4 hour hunt, you will need at least 2 sets and will be very low on the charge towards the end. This may be inconvenient for some.
The average rechargeable AA battery battery now has 2100 mah or 84% of the capacity of a Duracell AA alkaline. Given the 20 to 25 hour battery life of alkalines on the average AA powered metal detector, you will probably be able to hunt at least twice for 8 hours before needing to recharge. Not to mention that nimh will allow you to top off the charge once you get home and continue hunting indefinitely before a full charge. The downside hear is that nimh have a self discharge rate. It is best to use your rechargeables at the most a week after charging to get something close to the rated capacity. This is acceptable to some and incovenient for others. Its your choice.
NOTES ON SELF DISCHARGE:
Alkaline batteries stored at "room temperature" self discharge at a rate of less than two percent per year. So normally refrigerating or freezing them will only help maintain their charge by a tiny amount. Hardly worth the effort of chilling them. However, if alkaline batteries are stored at higher temperatures they will start to lose capacity much quicker. At 85 degrees F they only lose about 5% per year, but at 100 degrees they lose 25% per year. So if you live in a very hot climate or are storing your batteries in a very hot location, it may be worthwhile for you to store your alkaline batteries in a refrigerator instead.
NiMH and NiCd batteries self discharge at a MUCH faster rate than alkaline batteries. In fact, at "room temperature" (about 70 degrees F) NiMH and NiCD batteries will self discharge a few percent PER DAY. Storing them at lower temperatures will slow their self discharge rate dramatically. NiMH batteries stored at freezing will retain over 90% of their charge for full month. Water damages nimh batteries, so do not freeze them.
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