Posted by CANbike on Thu, 2 Jul 2015

Eveready Floating Lantern (5109LS) Modification

The following are instruction for modifying the 2014 Eveready Floating Lantern (5109LS) to significantly increase runtime past 500 hours.

Eveready Floating Lantern (5109LS)

The 6V floating lantern can be found at most retail stores or $7.97 or less.

It’s a great price for an emergency light as it is cheap, durable, long running, and simple to use.

Claimed FL 1 specs are 50 lumens / 100 h / 84 m with a Super Heavy Duty Lantern battery.

Eveready Floating Lantern

A Long Term Blackout Light?

Most major blackouts are only a couple of hours. However they are becoming more frequent and can last for weeks. For example, in 2012 the following power outages lasted for at least a week as a result of Superstorm Sandy.

Location Utility/Power Pool Name Duration (hours)
LONG ISLAND, N.Y. Long Island Power Authority (LIPA) 337 hours
NIAGARA COUNTY, N.Y. Somerset Operating Company 288 hours, 30 minutes
WEST VIRGINIA FirstEnergy Corp: Mon Power Company 287 hours, 59 minutes
GREATER NEW YORK CITY, N.Y. Consolidated Edison Co-NY Inc. 242 hours, 59 minutes
MARYLAND, WEST VIRGINIA FirstEnergy Corp: Potomac Edison 241 hours, 8 minutes
EASTERN PENNSYLVANIA FirstEnergy Corp: Met-Ed 223 hours, 48 minutes
MARYLAND, WEST VIRGINIA FirstEnergy: Potomac Edison 192 hours, 43 minutes
NEW JERSEY PSE&G 187 hours, 57 minutes
ATLANTIC CITY ELECTRIC SERVICE TERRITORY, N.J. Atlantic City Electric 184 hours, 18 minutes
GREATER CLEVELAND, OHIO FirstEnergy Corp: CEI 175 hours, 59 minutes

The Eveready Floating Lantern’s 100 hour runtime is insufficient. Fortunately it can be easily increased by five fold and still produce enough light for indoor use to outlast a 2 week power outage.*


Credit is given to luxstar for the article Easier Flashlight Mod Increases Run Time 3.6X.

V = I x R

  • Voltage = Current x Resistance

The current draw from the 5109LS LED is 185 mA. This can be reduced by adding a resistor. To figure out the resistor, the equation V = I x R is used.

Assuming the forward voltage of the LED is 3V, and the lantern battery is 6V, the voltage drop (battery voltage minus LED forward voltage) is

6V - 3V = 3V


3 = I x R

Solving for I,

I = 3 / R

Looking at my pack of resistors, the following currents were calculated,

Resister (ohm) Current (mA)
10 300
22 136
47 64
100 30
220 14
470 6
1000 3
2200 1

The 100 ohm resistor is ideal. An initial test with the resistor and the lantern produced 5-10 lumens of light, which is suitable for indoor use. In addition, the lower current draw will results in ~6x the runtime.

Modification Instructions


  • 2014 Eveready Floating Lantern (5109LS)
  • 100 ohm resistor
  • Soldering Iron
  • Solder
  • Wire clippers


  1. Open up the floating Lantern
    Open up the Eveready Floating Lantern
  2. Isolate the flashlight head and note the polarity
    Modify the Eveready 6V Lantern Head
  3. Lift the negative metal strip up and clip it with wire cutters
    Clip the Negative Lead
  4. Solder the 100 ohm resistor across the cut
    Solder the Resistor to Negative Lead


The modified lantern with 100 ohm resistor, measured a current draw of 31 mA. Excellent!
The original lantern measured a current draw of 185 mA, or a difference of 154 mA.

Based on general usage indoors, the original light appeared 2.5X as bright.

Modified vs Original Floating Lantern Beam Shot

The modified lantern is on the left, while an unmodified Eveready Floating Lantern (5109LS) is on the right.
Mod vs Original Eveready Floating Lantern


No runtime test were performed as it would take too long. However, estimated runtimes were calculated.

Method 1: Calculation Based on FL 1 Specs

Eveready claimed FL 1 specs are 50 lumens / 100 h with a Super Heavy Duty Lantern battery.

The measured current draw was 185 mA for the original lantern, and 31 mA for the modified lantern. Therefor the modified light should run 5.97, or (185 / 31), times as long on a Super Heavy Duty lantern battery.

100 hours x 5.97 = 597 hours

Method 2: Calculation Based on Wattage

Method 2 is rough and approximate due to current dropping as voltage drops. Calculate the power requirement of the LED in watts. Next, calculate the power supplied by the battery in watt*hours and divide it by the requirements of the LED.

An Eveready Super Heavy Duty lantern battery has a capacity of 9100 mAh at 100 mA.

Led requires 3V * I (watts). Battery provides 6V * 9.1 aH (watt*hours). Runtime = 6 * 9.1 watt*hours / (3 * I) watts

  • Example 1: Original Eveready Floating Lantern (5109LS) at 185 mA
    6*9.1/(3*0.185) = 98.37 hours
  • Example 2: Modified Lantern at 31 mA
    6*9.1/(3*0.031) = 587.10 hours
    587.10 hours / 24 = 24.46 days

  • Based on these calculations, the modified floating lantern will outlast a 3 week power outage using the included battery. Moreover, if it is used for only 6 hours per day, then it will last 3 months.

Replacement Battery

Lantern batteries are not created equally. The included 6V Super Heavy Duty lantern battery has up to half the capacity of an Alkaline lantern battery.

But not all Alkaline lantern batteries are equal either. Some are made of 4 D cells with a spacer. While others use 4 F cells to maximize capacity and space.

Lantern batteries made of 4D cells are inferior to 4F cells. They have smaller capacities even though they look the same.

Heavy Duty Alkaline 4D Alkaline 4F
Capacity (Ah) 9.1 15 19
@ 100 mA discharge
Weight (g) 600 665 885
Price $3-$7 $9.99+ $9.99
Modded Lantern 587 968 1226
Est. Runtime (h)

Ironically, it may be cheaper to buy a new floating lantern with a 6V battery.

Differentiate Heavy Duty from Alkaline 6V Battery

These are easy to differentiate.

  • They are labeled as either Heavy Duty (Carbon Zinc) or Alkaline.
  • Heavy Duties have a three year expiry date.
  • Alkalines have a 5 five year or greater expiry date.
  • Heavy Duties tend to be much cheaper.

Differentiate 6V Alkaline 4D from 4F Battery

These are trickier to differentiate.

  • 4F cells weigh 885g, 4D cells weigh 665g.
  • 6V 4D cells use spacers and are unbalanced. One end weighs more than the other.
  • 6V 4F cells are balanced. Tilt it to the side, and it will feel balanced in the center.

6V 4D cell lantern batteries should be avoided. It is more economical to buy a “4 D Cell to 6V Lantern Battery Adapter” and Alkaline D cells.


Avoid Duracell 6V batteries. They are overpriced 4D cells plus spacer packed into a 6V lantern battery container. They do not use F cells.


Eveready produces Heavy Duty 6V batteries. They clearly label their products as Heavy Duty. Buy them only if they are cheap.


Energizer produces Alkaline 6V batteries using either 4D (product code 529-4D) or 4F (product code 529-4F) cells. Look for the heavier, balanced, 6V lantern batteries to ensure 4F cells.


Rayovac produces Heavy Duty (“General Purpose” or “Heavy Duty” label), 4D cells (“Alkaline” label), and 4F cells (“Ultra Long-Lasting Alkaline” label) lantern batteries.

Always On Temporary Beacon

An always on beacon mode can be installed and removed easily by using a resistor to create a bridge from the negative metal strip to the positive metal strip.


A 100000 ohm resistor has been suggested, but the battery would expire long before it is drained. Lantern batteries past expiration have a much greater chance of leaking. As a result, an alternate resistor to match the battery shelf life was chosen.

Most Heavy Duty lantern batteries have an expiry date of 3 years.

Eveready Super-Heavy Duty 6V Battery Expiry Date

As a result,

3 years * 365 days/year * 24 hours/day = 26280 hours

At really low currents, the Eveready Super Heavy Duty Lantern Battery has a capacity of 11 Ah.

11 Ah / 26280 h = 0.000418569 A

Since V=IxR or R=V/I

3V / 0.000418569 A = 7167 ohms

Round up to a common resistor size of 10k ohms.

Two-Step Toolless Instructions:

  1. Take a 10k ohm and bend it into a U shape.
    Bend 10K ohm Resistor
  2. Insert it securely under the negative and positive metal strips.
    Insert 10K Resistor

Beacon Beam shot

  • Looking at the glowing LED.
    6V Floating Lantern Locater Light
  • An always on sub-lumen flashlight is highly visible during power outages.
    Locator Light Beam Shot

Estimated 10k ohm Runtime

The measured current with the 10k ohm resistor was 0.00039 A.

At really low currents, the Eveready Super Heavy Duty Lantern Battery has a capacity of 11 Ah. Expiry date of 3 years. Beacon runtime is,

11 Ah / 0.00039 A = 28205.13 h
28205.13 h / 24 h/day = 1175.21 days
1175.21 days / 365 days/year = 3.22 years

At really low currents, an Energizer 4F Cell Lantern Battery has a capacity of 26 Ah. Expiry date of 5-7 years. Beacon runtime is,

26 Ah / 0.00039 A = 66666.67 h
66666.67 h / 24 h/day = 2777.78 days
2777.78 days / 365 days/year = 7.61 years

Final Words

The 2014 Eveready Floating Lantern (5109LS) is an excellent emergency blackout flashlight. At least one should be purchased for an emergency preparedness kit as they are cheap, reliable, and durable.

An added bonus is the new design with metal strips. It makes it simple for modifying it into a longterm 500+ hour running flashlight.

For less than $8, or even $5 when on sale, this is a bargain blackout flashlight to buy. Even without the modification, it is worth the price.

Related Item(s): Review

Related Item(s): Articles

Related Item(s): Resource