此類充電器構造簡單：一般由電源變壓器和四個二極管構成的橋式整流電路組成。充電的整個過程電壓保持不變，當電池的內阻隨著充電過程越來越小，因此充電電流也越來越大，產生的熱量也越來越多。電池快充飽時發熱量最大。加速電解質的分解，從而縮短了電池的壽命。早期的廠家生產的充電器采(cai)取“小(xiao)心駛得萬年船”的策(ce)略，用(yong)小(xiao)電(dian)(dian)流(liu)充(chong)電(dian)(dian)，一般不超過(guo)100mA ，這樣電(dian)(dian)池充(chong)到最后，發熱不至于(yu)太大，從而延長(chang)電(dian)(dian)池壽(shou)命(ming)。缺(que)點是充(chong)電(dian)(dian)時(shi)(shi)間(jian)長(chang)。現(xian)在生產這類的廠家，采(cai)用(yong)中電(dian)(dian)流(liu)充(chong)電(dian)(dian)，100～200mA 充(chong)電(dian)(dian)時(shi)(shi)間(jian)大大縮短，但是以犧(xi)牲電(dian)(dian)池壽(shou)命(ming)為代價(jia)。傻瓜型充(chong)電(dian)(dian)器只能用(yong)時(shi)(shi)間(jian)來控制充(chong)電(dian)(dian)，它(ta)只適合于(yu)深(shen)充(chong)深(shen)放(fang)的五號、七號鎳(nie)鎘(ge)、鎳(nie)氫電(dian)(dian)池。

    充(chong)電(dian)(dian)時間(jian)：T = 1.5C/I（ C是(shi)電(dian)(dian)池容量，I是(shi)充(chong)電(dian)(dian)電(dian)(dian)流）例：如果有個1000mAh 的(de)電(dian)(dian)池放在充(chong)電(dian)(dian)電(dian)(dian)流是(shi)50mA的(de)充(chong)電(dian)(dian)器(qi)(qi)上充(chong)電(dian)(dian)，充(chong)電(dian)(dian)時間(jian)就是(shi)30小時。辨認這(zhe)類充(chong)電(dian)(dian)器(qi)(qi)的(de)方法：當插(cha)上電(dian)(dian)源插(cha)頭后，充(chong)電(dian)(dian)指示(shi)燈一(yi)直(zhi)亮著(zhu)。街上賣的(de)10～40元以內的(de)均是(shi)這(zhe)種充(chong)電(dian)(dian)器(qi)(qi)。